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            <h1>perlglossary</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#VERSION">VERSION</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#A">A</a><li><a href="#B">B</a><li><a href="#C">C</a><li><a href="#D">D</a><li><a href="#E">E</a><li><a href="#F">F</a><li><a href="#G">G</a><li><a href="#H">H</a><li><a href="#I">I</a><li><a href="#J">J</a><li><a href="#K">K</a><li><a href="#L">L</a><li><a href="#M">M</a><li><a href="#N">N</a><li><a href="#O">O</a><li><a href="#P">P</a><li><a href="#Q">Q</a><li><a href="#R">R</a><li><a href="#S">S</a><li><a href="#T">T</a><li><a href="#U">U</a><li><a href="#V">V</a><li><a href="#W">W</a><li><a href="#X">X</a><li><a href="#Y">Y</a><li><a href="#Z">Z</a></ul><li><a href="#AUTHOR-AND-COPYRIGHT">AUTHOR AND COPYRIGHT</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>perlglossary - Perl Glossary</p>
<a name="VERSION"></a><h1>VERSION</h1>
<p>version 5.021011</p>
<a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>A glossary of terms (technical and otherwise) used in the Perl
documentation, derived from the Glossary of <i>Programming
Perl</i>, Fourth Edition.  Words or phrases in bold are defined elsewhere in
this glossary.</p>
<p>Other useful sources include the Unicode Glossary <a href="http://unicode.org/glossary/">http://unicode.org/glossary/</a>,
the Free On-Line Dictionary of Computing <a href="http://foldoc.org/">http://foldoc.org/</a>,
the Jargon File <a href="http://catb.org/~esr/jargon/">http://catb.org/~esr/jargon/</a>,
and Wikipedia <a href="http://www.wikipedia.org/">http://www.wikipedia.org/</a>.</p>
<a name="A"></a><h2>A</h2>
<ul>
<li><a name="accessor-methods"></a><b>accessor methods</b>
<p>A <b>method</b> used to
indirectly inspect or update an <b>object</b>&#x2019;s state (its <b>instance
variables</b>).</p>
</li>
<li><a name="actual-arguments"></a><b>actual arguments</b>
<p>The <b>scalar values</b> that you supply
to a <b>function</b> or <b>subroutine</b> when you call it. For instance, when you
call <code class="inline"><span class="i">power</span><span class="s">(</span><span class="q">&quot;puff&quot;</span><span class="s">)</span></code>
, the string <code class="inline"><span class="q">&quot;puff&quot;</span></code>
 is the actual argument. See also
<b>argument</b> and <b>formal arguments</b>.</p>
</li>
<li><a name="address-operator"></a><b>address operator</b>
<p>Some languages work directly with the memory addresses of
values, but this can be like playing with fire. Perl provides a set of
asbestos gloves for handling all memory management. The closest to an
address operator in Perl is the backslash operator, but it gives you a
<b>hard reference</b>, which is much safer than a memory address.</p>
</li>
<li><a name="algorithm"></a><b>algorithm</b>
<p>A well-defined sequence of steps, explained clearly
enough that even a computer could do them.</p>
</li>
<li><a name="alias"></a><b>alias</b>
<p>A nickname for something, which behaves in all ways as
though you&#x2019;d used the original name instead of the nickname. Temporary
aliases are implicitly created in the loop variable for <code class="inline">foreach</code>
 loops, in
the <code class="inline"><span class="i">$_</span></code>
 variable for <code class="inline"><a class="l_k" href="functions/map.html">map</a></code> or <code class="inline"><a class="l_k" href="functions/grep.html">grep</a></code> operators, in <code class="inline"><span class="i">$a</span></code>
 and <code class="inline"><span class="i">$b</span></code>

during <code class="inline"><a class="l_k" href="functions/sort.html">sort</a></code>&#x2019;s comparison function, and in each element of <code class="inline"><span class="i">@_</span></code>
 for the
<b>actual arguments</b> of a subroutine call. Permanent aliases are explicitly
created in <b>packages</b> by <b>importing</b> symbols or by assignment to
<b>typeglobs</b>. Lexically scoped aliases for package variables are explicitly
created by the <code class="inline"><a class="l_k" href="functions/our.html">our</a></code> declaration.</p>
</li>
<li><a name="alphabetic"></a><b>alphabetic</b>
<p>The sort of characters we put into words. In Unicode, this
is all letters including all ideographs and certain diacritics, letter
numbers like Roman numerals, and various combining marks.</p>
</li>
<li><a name="alternatives"></a><b>alternatives</b>
<p>A list of possible choices from which you may
select only one, as in, &#x201c;Would you like door A, B, or C?&#x201d; Alternatives in
regular expressions are separated with a single vertical bar: <code class="inline">|</code>.
Alternatives in normal Perl expressions are separated with a double vertical
bar: <code class="inline">||</code>. Logical alternatives in <b>Boolean</b> expressions are separated
with either <code class="inline">||</code> or <code class="inline">or</code>
.</p>
</li>
<li><a name="anonymous"></a><b>anonymous</b>
<p>Used to describe a <b>referent</b>
that is not directly accessible through a named <b>variable</b>. Such a referent
must be indirectly accessible through at least one <b>hard reference</b>. When
the last hard reference goes away, the anonymous referent is destroyed
without pity.</p>
</li>
<li><a name="application"></a><b>application</b>
<p>A bigger, fancier sort of <b>program</b> with a fancier
name so people don&#x2019;t realize they are using a program.</p>
</li>
<li><a name="architecture"></a><b>architecture</b>
<p>The kind of computer you&#x2019;re working on, where one &#x201c;kind of
computer&#x201d; means all those computers sharing a compatible machine language.
Since Perl programs are (typically) simple text files, not executable
images, a Perl program is much less sensitive to the architecture it&#x2019;s
running on than programs in other languages, such as C, that are <b>compiled</b>
into machine code. See also <b>platform</b> and <b>operating system</b>.</p>
</li>
<li><a name="argument"></a><b>argument</b>
<p>A piece of data supplied to a <b>program</b>,
<b>subroutine</b>, <b>function</b>, or <b>method</b> to tell it what it&#x2019;s supposed to
do. Also called a &#x201c;parameter&#x201d;.</p>
</li>
<li><a name="ARGV"></a><b>ARGV</b>
<p>The name of the array containing the <b>argument</b> <b>vector</b>
from the command line. If you use the empty <code class="inline">&lt;&gt;</code>
 operator, <code class="inline"><span class="w">ARGV</span></code>

is the name of both the <b>filehandle</b> used to traverse the arguments and the
<b>scalar</b> containing the name of the current input file.</p>
</li>
<li><a name="arithmetical-operator"></a><b>arithmetical operator</b>
<p>A <b>symbol</b> such as <code class="inline">+</code>
 or <code class="inline">/</code> that tells
Perl to do the arithmetic you were supposed to learn in grade school.</p>
</li>
<li><a name="array"></a><b>array</b>
<p>An ordered sequence of <b>values</b>, stored such that you can
easily access any of the values using an <i>integer subscript</i> that specifies
the value&#x2019;s <b>offset</b> in the sequence.</p>
</li>
<li><a name="array-context"></a><b>array context</b>
<p>An archaic expression for what is more correctly referred to
as <b>list context</b>.</p>
</li>
<li><a name="Artistic-License"></a><b>Artistic License</b>
<p>The open source license that Larry Wall
created for Perl, maximizing Perl&#x2019;s usefulness, availability, and
modifiability. The current version is 2. (<a href="http://www.opensource.org/licenses/artistic-license.php">http://www.opensource.org/licenses/artistic-license.php</a>).</p>
</li>
<li><a name="ASCII"></a><b>ASCII</b>
<p>The American Standard Code for
Information Interchange (a 7-bit character set adequate only for poorly
representing English text). Often used loosely to describe the lowest 128
values of the various ISO-8859-X character sets, a bunch of mutually
incompatible 8-bit codes best described as half ASCII. See also <b>Unicode</b>.</p>
</li>
<li><a name="assertion"></a><b>assertion</b>
<p>A component of a <b>regular expression</b> that must be true for the pattern to
match but does not necessarily match any characters itself. Often used
specifically to mean a <b>zero-width</b> assertion.</p>
</li>
<li><a name="assignment"></a><b>assignment</b>
<p>An <b>operator</b> whose assigned mission in life is to
change the value of a <b>variable</b>.</p>
</li>
<li><a name="assignment-operator"></a><b>assignment operator</b>
<p>Either a regular <b>assignment</b> or a compound
<b>operator</b> composed of an ordinary assignment and some other operator, that
changes the value of a variable in place; that is, relative to its old
value. For example, <code class="inline"><span class="i">$a</span> += <span class="n">2</span></code>
 adds <code class="inline"><span class="n">2</span></code>
 to <code class="inline"><span class="i">$a</span></code>
.</p>
</li>
<li><a name="associative-array"></a><b>associative array</b>
<p>See <b>hash</b>. Please. The term associative array is the
old Perl 4 term for a <b>hash</b>. Some languages call it a dictionary.</p>
</li>
<li><a name="associativity"></a><b>associativity</b>
<p>Determines whether you do the left <b>operator</b> first or the
right <b>operator</b> first when you have &#x201c;A <b>operator</b> B <b>operator</b> C&#x201d;, and
the two operators are of the same precedence. Operators like <code class="inline">+</code>
 are left
associative, while operators like <code class="inline"><span class="i">**</span></code>
 are right associative. See Camel
chapter 3, &#x201c;Unary and Binary Operators&#x201d; for a list of operators and their
associativity.</p>
</li>
<li><a name="asynchronous"></a><b>asynchronous</b>
<p>Said of events or activities whose relative
temporal ordering is indeterminate because too many things are going on at
once. Hence, an asynchronous event is one you didn&#x2019;t know when to expect.</p>
</li>
<li><a name="atom"></a><b>atom</b>
<p>A <b>regular expression</b> component potentially matching a
<b>substring</b> containing one or more characters and treated as an indivisible
syntactic unit by any following <b>quantifier</b>. (Contrast with an
<b>assertion</b> that matches something of <b>zero width</b> and may not be quantified.)</p>
</li>
<li><a name="atomic-operation"></a><b>atomic operation</b>
<p>When Democritus gave the word &#x201c;atom&#x201d; to the indivisible
bits of matter, he meant literally something that could not be cut: <i>&#x1f00;-</i>
(not) + <i>-&#x3c4;&#x3bf;&#x3bc;&#x3bf;&#x3c2;</i> (cuttable). An atomic operation is an action that can&#x2019;t be
interrupted, not one forbidden in a nuclear-free zone.</p>
</li>
<li><a name="attribute"></a><b>attribute</b>
<p>A new feature that allows the declaration of
<b>variables</b> and <b>subroutines</b> with modifiers, as in <code class="inline"><a name="foo"></a>sub <span class="m">foo</span> <span class="co">:</span> <span class="w">locked</span>
<span class="w">method</span></code>
. Also another name for an <b>instance variable</b> of an <b>object</b>.</p>
</li>
<li><a name="autogeneration"></a><b>autogeneration</b>
<p>A feature of <b>operator overloading</b> of <b>objects</b>,
whereby the behavior of certain <b>operators</b> can be reasonably deduced using
more fundamental operators. This assumes that the overloaded operators will
often have the same relationships as the regular operators. See Camel
chapter 13, &#x201c;Overloading&#x201d;.</p>
</li>
<li><a name="autoincrement"></a><b>autoincrement</b>
<p>To add one to something automatically, hence the name
of the <code class="inline">++</code>
 operator. To instead subtract one from something automatically
is known as an &#x201c;autodecrement&#x201d;.</p>
</li>
<li><a name="autoload"></a><b>autoload</b>
<p>To load on demand. (Also called &#x201c;lazy&#x201d; loading.)
Specifically, to call an <code class="inline">AUTOLOAD</code>
 subroutine on behalf of an undefined
subroutine.</p>
</li>
<li><a name="autosplit"></a><b>autosplit</b>
<p>To split a string automatically, as the <i>&#x2013;a</i> <b>switch</b>
does when running under <i>&#x2013;p</i> or <i>&#x2013;n</i> in order to emulate <b>awk</b>. (See also
the <code class="inline"><span class="w">AutoSplit</span></code>
 module, which has nothing to do with the
<code class="inline"><span class="q">&ndash;a</span></code>
 switch but a lot to do with autoloading.)</p>
</li>
<li><a name="autovivification"></a><b>autovivification</b>
<p>A Graeco-Roman word meaning &#x201c;to bring oneself to life&#x201d;.
In Perl, storage locations (<b>lvalues</b>) spontaneously generate themselves as
needed, including the creation of any <b>hard reference</b> values to point to
the next level of storage. The assignment <code class="inline"><span class="i">$a</span>[<span class="n">5</span>][<span class="n">5</span>][<span class="n">5</span>][<span class="n">5</span>][<span class="n">5</span>] = <span class="q">&quot;quintet&quot;</span></code>

potentially creates five scalar storage locations, plus four references (in
the first four scalar locations) pointing to four new anonymous arrays (to
hold the last four scalar locations). But the point of autovivification is
that you don&#x2019;t have to worry about it.</p>
</li>
<li><a name="AV"></a><b>AV</b>
<p>Short for &#x201c;array
value&#x201d;, which refers to one of Perl&#x2019;s internal data types that holds an
<b>array</b>. The <code class="inline"><span class="w">AV</span></code>
 type is a subclass of <b>SV</b>.</p>
</li>
<li><a name="awk"></a><b>awk</b>
<p>Descriptive editing term&#x2014;short for &#x201c;awkward&#x201d;. Also
coincidentally refers to a venerable text-processing language from which
Perl derived some of its high-level ideas.</p>
</li>
</ul>
<a name="B"></a><h2>B</h2>
<ul>
<li><a name="backreference"></a><b>backreference</b>
<p>A substring <b>captured</b>
by a subpattern within unadorned parentheses in a <b>regex</b>. Backslashed
decimal numbers (<code class="inline">\<span class="n">1</span></code>
, <code class="inline">\<span class="n">2</span></code>
, etc.) later in the same pattern refer back to
the corresponding subpattern in the current match. Outside the pattern, the
numbered variables (<code class="inline"><span class="i">$1</span></code>
, <code class="inline"><span class="i">$2</span></code>
, etc.) continue to refer to these same
values, as long as the pattern was the last successful match of the current
<b>dynamic scope</b>.</p>
</li>
<li><a name="backtracking"></a><b>backtracking</b>
<p>The practice of saying, &#x201c;If I had to do it all over, I&#x2019;d do
it differently,&#x201d; and then actually going back and doing it all over
differently. Mathematically speaking, it&#x2019;s returning from an unsuccessful
recursion on a tree of possibilities. Perl backtracks when it attempts to
match patterns with a <b>regular expression</b>, and its earlier attempts don&#x2019;t
pan out. See the section &#x201c;The Little Engine That /Couldn(n&#x2019;t)&#x201d; in Camel
chapter 5, &#x201c;Pattern Matching&#x201d;.</p>
</li>
<li><a name="backward-compatibility"></a><b>backward compatibility</b>
<p>Means you can still run your old program
because we didn&#x2019;t break any of the features or bugs it was relying on.</p>
</li>
<li><a name="bareword"></a><b>bareword</b>
<p>A word sufficiently ambiguous to be deemed illegal under
<code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&#39;subs&#39;</span></code>
. In the absence of that stricture, a bareword is
treated as if quotes were around it.</p>
</li>
<li><a name="base-class"></a><b>base class</b>
<p>A generic <b>object</b> type; that is, a <b>class</b>
from which other, more specific classes are derived genetically by
<b>inheritance</b>. Also called a
&#x201c;superclass&#x201d; by people who respect their ancestors.</p>
</li>
<li><a name="big-endian"></a><b>big-endian</b>
<p>From Swift: someone who
eats eggs big end first. Also used of computers that store the most
significant <b>byte</b> of a word at a lower byte address than the least
significant byte. Often considered superior to little-endian machines. See
also <b>little-endian</b>.</p>
</li>
<li><a name="binary"></a><b>binary</b>
<p>Having to do with numbers represented in base 2. That means
there&#x2019;s basically two numbers: 0 and 1. Also used to describe a file of
&#x201c;nontext&#x201d;, presumably because such a file makes full use of all the binary
bits in its bytes. With the advent of <b>Unicode</b>, this distinction, already
suspect, loses even more of its meaning.</p>
</li>
<li><a name="binary-operator"></a><b>binary operator</b>
<p>An <b>operator</b> that takes two <b>operands</b>.</p>
</li>
<li><a name="bind"></a><b>bind</b>
<p>To assign a specific <b>network address</b> to a <b>socket</b>.</p>
</li>
<li><a name="bit"></a><b>bit</b>
<p>An integer in the range from 0 to 1, inclusive. The smallest
possible unit of information storage. An eighth of a <b>byte</b> or of a dollar.
(The term &#x201c;Pieces of Eight&#x201d; comes from being able to split the old Spanish
dollar into 8 bits, each of which still counted for money. That&#x2019;s why a 25-
cent piece today is still &#x201c;two bits&#x201d;.)</p>
</li>
<li><a name="bit-shift"></a><b>bit shift</b>
<p>The movement of bits left or right in a
computer word, which has the effect of multiplying or dividing by a
power of 2.</p>
</li>
<li><a name="bit-string"></a><b>bit string</b>
<p>A sequence of <b>bits</b> that is actually being thought of as a
sequence of bits, for once.</p>
</li>
<li><a name="bless"></a><b>bless</b>
<p>In corporate life, to grant official
approval to a thing, as in, &#x201c;The VP of Engineering has blessed our
WebCruncher project.&#x201d; Similarly, in Perl, to grant official approval to a
<b>referent</b> so that it can function as an <b>object</b>, such as a WebCruncher
object. See the <code class="inline"><a class="l_k" href="functions/bless.html">bless</a></code> function in Camel chapter 27, &#x201c;Functions&#x201d;.</p>
</li>
<li><a name="block"></a><b>block</b>
<p>What a <b>process</b> does when it has to wait for something:
&#x201c;My process blocked waiting for the disk.&#x201d; As an unrelated noun, it refers
to a large chunk of data, of a size that the <b>operating system</b> likes to
deal with (normally a power of 2 such as 512 or 8192). Typically refers to
a chunk of data that&#x2019;s coming from or going to a disk file.</p>
</li>
<li><a name="BLOCK"></a><b>BLOCK</b>
<p>A syntactic construct
consisting of a sequence of Perl <b>statements</b> that is delimited by braces.
The <code class="inline">if</code>
 and <code class="inline">while</code>
 statements are defined in terms of <i><code class="inline"><span class="w">BLOCK</span></code>
</i>s, for
instance. Sometimes we also say &#x201c;block&#x201d; to mean a lexical scope; that is, a
sequence of statements that acts like a <i><code class="inline"><span class="w">BLOCK</span></code>
</i>, such as within an
<code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code> or a file, even though the statements aren&#x2019;t delimited by braces.</p>
</li>
<li><a name="block-buffering"></a><b>block buffering</b>
<p>A method of making input and output
efficient by passing one <b>block</b> at a time. By default, Perl does block
buffering to disk files. See <b>buffer</b> and <b>command buffering</b>.</p>
</li>
<li><a name="Boolean"></a><b>Boolean</b>
<p>A value that is either <b>true</b> or
<b>false</b>.</p>
</li>
<li><a name="Boolean-context"></a><b>Boolean context</b>
<p>A special kind of <b>scalar
context</b> used in conditionals to decide whether the <b>scalar value</b> returned
by an expression is <b>true</b> or <b>false</b>. Does not evaluate as either a
string or a number. See <b>context</b>.</p>
</li>
<li><a name="breakpoint"></a><b>breakpoint</b>
<p>A spot in your program where you&#x2019;ve told the debugger
to stop <b>execution</b> so you can poke around and see whether anything is
wrong yet.</p>
</li>
<li><a name="broadcast"></a><b>broadcast</b>
<p>To send a <b>datagram</b> to multiple destinations
simultaneously.</p>
</li>
<li><a name="BSD"></a><b>BSD</b>
<p>A psychoactive drug, popular in the &#x2019;80s, probably developed at UC
Berkeley or thereabouts. Similar in many ways to the prescription-only
medication called &#x201c;System V&#x201d;, but infinitely more useful. (Or, at least,
more fun.) The full chemical name is &#x201c;Berkeley Standard Distribution&#x201d;.</p>
</li>
<li><a name="bucket"></a><b>bucket</b>
<p>A location in a <b>hash table</b> containing (potentially)
multiple entries whose keys &#x201c;hash&#x201d; to the same hash value according to its
hash function. (As internal policy, you don&#x2019;t have to worry about it unless
you&#x2019;re into internals, or policy.)</p>
</li>
<li><a name="buffer"></a><b>buffer</b>
<p>A temporary holding location for data. Data that are
<b>Block buffering</b> means that the data is passed on to its destination
whenever the buffer is full. <b>Line buffering</b> means that it&#x2019;s passed on
whenever a complete line is received. <b>Command buffering</b> means that it&#x2019;s
passed every time you do a <code class="inline"><a class="l_k" href="functions/print.html">print</a></code> command (or equivalent). If your output
is unbuffered, the system processes it one byte at a time without the use of
a holding area. This can be rather inefficient.</p>
</li>
<li><a name="built-in"></a><b>built-in</b>
<p>A <b>function</b> that is predefined in the
language. Even when hidden by <b>overriding</b>, you can always get at a built-
in function by <b>qualifying</b> its name with the <code class="inline"><span class="w">CORE::</span></code>
 pseudopackage.</p>
</li>
<li><a name="bundle"></a><b>bundle</b>
<p>A group of related modules on <b>CPAN</b>. (Also sometimes
refers to a group of command-line switches grouped into one <b>switch
cluster</b>.)</p>
</li>
<li><a name="byte"></a><b>byte</b>
<p>A piece of data worth eight <b>bits</b> in most places.</p>
</li>
<li><a name="bytecode"></a><b>bytecode</b>
<p>A pidgin-like lingo spoken among &#x2019;droids when they don&#x2019;t wish to reveal
their orientation (see <b>endian</b>). Named after some similar languages spoken
(for similar reasons) between compilers and interpreters in the late 20&#x1d57;&#x2b0;
century. These languages are characterized by representing everything as a
nonarchitecture-dependent sequence of bytes.</p>
</li>
</ul>
<a name="C"></a><h2>C</h2>
<ul>
<li><a name="C"></a><b>C</b>
<p>A language beloved by many for its inside-out <b>type</b>
definitions, inscrutable <b>precedence</b> rules, and heavy <b>overloading</b> of
the function-call mechanism. (Well, actually, people first switched to C
because they found lowercase identifiers easier to read than upper.) Perl is
written in C, so it&#x2019;s not surprising that Perl borrowed a few ideas from it.</p>
</li>
<li><a name="cache"></a><b>cache</b>
<p>A data repository. Instead of computing expensive answers
several times, compute it once and save the result.</p>
</li>
<li><a name="callback"></a><b>callback</b>
<p>A <b>handler</b> that you register with some other part of your
program in the hope that the other part of your program will <b>trigger</b> your
handler when some event of interest transpires.</p>
</li>
<li><a name="call-by-reference"></a><b>call by reference</b>
<p>An <b>argument</b>-passing mechanism in which the <b>formal arguments</b> refer directly to the
<b>actual arguments</b>, and the <b>subroutine</b> can change the actual arguments
by changing the formal arguments. That is, the formal argument is an
<b>alias</b> for the actual argument. See also <b>call by value</b>.</p>
</li>
<li><a name="call-by-value"></a><b>call by value</b>
<p>An <b>argument</b>-passing mechanism in which the <b>formal
arguments</b> refer to a copy of the <b>actual arguments</b>, and the
<b>subroutine</b> cannot change the actual arguments by changing the formal
arguments. See also <b>call by reference</b>.</p>
</li>
<li><a name="canonical"></a><b>canonical</b>
<p>Reduced to a standard form to facilitate comparison.</p>
</li>
<li><a name="capture-variables"></a><b>capture variables</b>
<p>The variables&#x2014;such as <code class="inline"><span class="i">$1</span></code>
 and
<code class="inline"><span class="i">$2</span></code>
, and <code class="inline"><span class="i">%+</span></code>
 and <code class="inline"><span class="i">%&ndash;</span> </code>
&#x2014;that hold the text remembered in a pattern
match. See Camel chapter 5, &#x201c;Pattern Matching&#x201d;.</p>
</li>
<li><a name="capturing"></a><b>capturing</b>
<p>The use of parentheses around a <b>subpattern</b> in a
<b>regular expression</b> to store the matched <b>substring</b> as a
<b>backreference</b>. (Captured strings are also returned as a list in <b>list
context</b>.) See Camel chapter 5, &#x201c;Pattern Matching&#x201d;.</p>
</li>
<li><a name="cargo-cult"></a><b>cargo cult</b>
<p>Copying and pasting code without understanding it, while
superstitiously believing in its value. This term originated from
preindustrial cultures dealing with the detritus of explorers and colonizers
of technologically advanced cultures. See <i>The Gods Must Be Crazy</i>.</p>
</li>
<li><a name="case"></a><b>case</b>
<p>A property of certain
characters. Originally, typesetter stored capital letters in the upper of
two cases and small letters in the lower one. Unicode recognizes three
cases: <b>lowercase</b> (<b>character property</b> <code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">lower</span><span class="s">}</span></code>
), <b>titlecase</b>
(<code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">title</span><span class="s">}</span></code>
), and <b>uppercase</b> (<code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">upper</span><span class="s">}</span></code>
). A fourth casemapping called
<b>foldcase</b> is not itself a distinct case, but it is used internally to
implement <b>casefolding</b>. Not all letters have case, and some nonletters
have case.</p>
</li>
<li><a name="casefolding"></a><b>casefolding</b>
<p>Comparing or matching a string case-insensitively. In Perl, it
is implemented with the <code class="inline">/i</code> pattern modifier, the <code class="inline"><a class="l_k" href="functions/fc.html">fc</a></code> function, and the
<code class="inline">\<span class="w">F</span></code>
 double-quote translation escape.</p>
</li>
<li><a name="casemapping"></a><b>casemapping</b>
<p>The process of converting a string to one of the four Unicode
<b>casemaps</b>; in Perl, it is implemented with the <code class="inline"><a class="l_k" href="functions/fc.html">fc</a></code>, <code class="inline"><a class="l_k" href="functions/lc.html">lc</a></code>, <code class="inline"><a class="l_k" href="functions/ucfirst.html">ucfirst</a></code>,
and <code class="inline"><a class="l_k" href="functions/uc.html">uc</a></code> functions.</p>
</li>
<li><a name="character"></a><b>character</b>
<p>The smallest individual element of a string. Computers
store characters as integers, but Perl lets you operate on them as text. The
integer used to represent a particular character is called that character&#x2019;s
<b>codepoint</b>.</p>
</li>
<li><a name="character-class"></a><b>character class</b>
<p>A square-bracketed list of
characters used in a <b>regular expression</b> to indicate that any character
of the set may occur at a given point. Loosely, any predefined set of
characters so used.</p>
</li>
<li><a name="character-property"></a><b>character property</b>
<p>A predefined <b>character class</b> matchable by the <code class="inline">\<span class="w">p</span></code>

or <code class="inline">\<span class="w">P</span></code>
 <b>metasymbol</b>. <b>Unicode</b> defines hundreds of standard properties
for every possible codepoint, and Perl defines a few of its own, too.</p>
</li>
<li><a name="circumfix-operator"></a><b>circumfix operator</b>
<p>An <b>operator</b> that surrounds its <b>operand</b>, like the
angle operator, or parentheses, or a hug.</p>
</li>
<li><a name="class"></a><b>class</b>
<p>A user-defined <b>type</b>, implemented in Perl via a
<b>package</b> that provides (either directly or by inheritance) <b>methods</b>
(that is, <b>subroutines</b>) to handle <b>instances</b> of the class (its
<b>objects</b>). See also <b>inheritance</b>.</p>
</li>
<li><a name="class-method"></a><b>class method</b>
<p>A <b>method</b> whose <b>invocant</b> is a
<b>package</b> name, not an <b>object</b> reference. A method associated with the
class as a whole. Also see <b>instance method</b>.</p>
</li>
<li><a name="client"></a><b>client</b>
<p>In networking, a <b>process</b> that
initiates contact with a <b>server</b> process in order to exchange data and
perhaps receive a service.</p>
</li>
<li><a name="closure"></a><b>closure</b>
<p>An <b>anonymous</b> subroutine
that, when a reference to it is generated at runtime, keeps track of the
identities of externally visible <b>lexical variables</b>, even after those
lexical variables have supposedly gone out of <b>scope</b>. They&#x2019;re called
&#x201c;closures&#x201d; because this sort of behavior gives mathematicians a sense of
closure.</p>
</li>
<li><a name="cluster"></a><b>cluster</b>
<p>A parenthesized <b>subpattern</b>
used to group parts of a <b>regular expression</b> into a single <b>atom</b>.</p>
</li>
<li><a name="CODE"></a><b>CODE</b>
<p>The word returned by the <code class="inline"><a class="l_k" href="functions/ref.html">ref</a></code>
function when you apply it to a reference to a subroutine. See also <b>CV</b>.</p>
</li>
<li><a name="code-generator"></a><b>code generator</b>
<p>A system that writes code for you in a low-level
language, such as code to implement the backend of a compiler. See <b>program
generator</b>.</p>
</li>
<li><a name="codepoint"></a><b>codepoint</b>
<p>The integer a computer uses to represent a given
character. ASCII codepoints are in the range 0 to 127; Unicode codepoints
are in the range 0 to 0x1F_FFFF; and Perl codepoints are in the range 0 to
2&#xb3;&#xb2;&#x2212;1 or 0 to 2&#x2076;&#x2074;&#x2212;1, depending on your native integer size. In Perl Culture,
sometimes called <b>ordinals</b>.</p>
</li>
<li><a name="code-subpattern"></a><b>code subpattern</b>
<p>A <b>regular expression</b> subpattern
whose real purpose is to execute some Perl code&#x2014;for example, the <code class="inline">(?{...})</code>
and <code class="inline"><span class="s">(</span><span class="q">??</span><span class="s">{</span>...<span class="s">}</span><span class="s">)</span></code>
 subpatterns.</p>
</li>
<li><a name="collating-sequence"></a><b>collating sequence</b>
<p>The order into which <b>characters</b>
sort. This is used by <b>string</b> comparison routines to decide, for example,
where in this glossary to put &#x201c;collating sequence&#x201d;.</p>
</li>
<li><a name="co-maintainer"></a><b>co-maintainer</b>
<p>A person with permissions to index a <b>namespace</b> in
<b>PAUSE</b>. Anyone can upload any namespace, but only primary and
co-maintainers get their contributions indexed.</p>
</li>
<li><a name="combining-character"></a><b>combining character</b>
<p>Any character with the
General Category of Combining Mark (<code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">GC</span>=<span class="w">M</span><span class="s">}</span></code>
), which may be spacing or
nonspacing. Some are even invisible. A sequence of combining characters
following a grapheme base character together make up a single user-visible
character called a <b>grapheme</b>. Most but not all diacritics are combining
characters, and vice versa.</p>
</li>
<li><a name="command"></a><b>command</b>
<p>In <b>shell</b> programming, the syntactic combination of a
program name and its arguments. More loosely, anything you type to a shell
(a command interpreter) that starts it doing something. Even more loosely, a
Perl <b>statement</b>, which might start with a <b>label</b> and typically ends with
a semicolon.</p>
</li>
<li><a name="command-buffering"></a><b>command buffering</b>
<p>A mechanism in Perl that lets you
store up the output of each Perl <b>command</b> and then flush it out as a
single request to the <b>operating system</b>. It&#x2019;s enabled by setting the <code class="inline"><span class="i">$|</span></code>

(<code class="inline"><span class="i">$AUTOFLUSH</span></code>
) variable to a true value. It&#x2019;s used when you don&#x2019;t want data
sitting around, not going where it&#x2019;s supposed to, which may happen because
the default on a <b>file</b> or <b>pipe</b> is to use <b>block buffering</b>.</p>
</li>
<li><a name="command-line-arguments"></a><b>command-line arguments</b>
<p>The <b>values</b> you supply
along with a program name when you tell a <b>shell</b> to execute a <b>command</b>.
These values are passed to a Perl program through <code class="inline"><span class="i">@ARGV</span></code>
.</p>
</li>
<li><a name="command-name"></a><b>command name</b>
<p>The name of the program currently executing, as typed on the
command line. In C, the <b>command</b> name is passed to the program as the
first command-line argument. In Perl, it comes in separately as <code class="inline"><span class="i">$0</span></code>
.</p>
</li>
<li><a name="comment"></a><b>comment</b>
<p>A remark that doesn&#x2019;t affect the meaning of the program.
In Perl, a comment is introduced by a <code class="inline"><span class="c">#</span></code>
 character and continues to the
end of the line.</p>
</li>
<li><a name="compilation-unit"></a><b>compilation unit</b>
<p>The <b>file</b> (or <b>string</b>, in the case of <code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code>) that
is currently being <b>compiled</b>.</p>
</li>
<li><a name="compile"></a><b>compile</b>
<p>The process of turning source code into a machine-usable form. See <b>compile
phase</b>.</p>
</li>
<li><a name="compile-phase"></a><b>compile phase</b>
<p>Any time before Perl starts running your main
program. See also <b>run phase</b>. Compile phase is mostly spent in <b>compile
time</b>, but may also be spent in <b>runtime</b> when <code class="inline">BEGIN</code>
 blocks, <code class="inline"><a class="l_k" href="functions/use.html">use</a></code> or
<code class="inline"><a class="l_k" href="functions/no.html">no</a></code> declarations, or constant subexpressions are being evaluated. The
startup and import code of any <code class="inline"><a class="l_k" href="functions/use.html">use</a></code> declaration is also run during
compile phase.</p>
</li>
<li><a name="compiler"></a><b>compiler</b>
<p>Strictly speaking, a program that munches
up another program and spits out yet another file containing the program in
a &#x201c;more executable&#x201d; form, typically containing native machine instructions.
The <i>perl</i> program is not a compiler by this definition, but it does
contain a kind of compiler that takes a program and turns it into a more
executable form (<b>syntax trees</b>) within the <i>perl</i> process itself, which
the <b>interpreter</b> then interprets. There are, however, extension <b>modules</b>
to get Perl to act more like a &#x201c;real&#x201d; compiler. See Camel chapter 16,
&#x201c;Compiling&#x201d;.</p>
</li>
<li><a name="compile-time"></a><b>compile time</b>
<p>The time when Perl is trying to make sense of your
code, as opposed to when it thinks it knows what your code means and is
merely trying to do what it thinks your code says to do, which is <b>runtime</b>.</p>
</li>
<li><a name="composer"></a><b>composer</b>
<p>A &#x201c;constructor&#x201d; for a <b>referent</b> that isn&#x2019;t really an
<b>object</b>, like an anonymous array or a hash (or a sonata, for that matter).
For example, a pair of braces acts as a composer for a hash, and a pair of
brackets acts as a composer for an array. See the section &#x201c;Creating
References&#x201d; in Camel chapter 8, &#x201c;References&#x201d;.</p>
</li>
<li><a name="concatenation"></a><b>concatenation</b>
<p>The process of gluing one
cat&#x2019;s nose to another cat&#x2019;s tail. Also a similar operation on two
<b>strings</b>.</p>
</li>
<li><a name="conditional"></a><b>conditional</b>
<p>Something &#x201c;iffy&#x201d;. See <b>Boolean context</b>.</p>
</li>
<li><a name="connection"></a><b>connection</b>
<p>In telephony, the temporary electrical circuit between
the caller&#x2019;s and the callee&#x2019;s phone. In networking, the same kind of
temporary circuit between a <b>client</b> and a <b>server</b>.</p>
</li>
<li><a name="construct"></a><b>construct</b>
<p>As a noun, a piece of syntax made up of smaller
pieces. As a transitive verb, to create an <b>object</b> using a <b>constructor</b>.</p>
</li>
<li><a name="constructor"></a><b>constructor</b>
<p>Any <b>class method</b>, <b>instance</b>, or <b>subroutine</b>
that composes, initializes, blesses, and returns an <b>object</b>. Sometimes we
use the term loosely to mean a <b>composer</b>.</p>
</li>
<li><a name="context"></a><b>context</b>
<p>The surroundings or environment. The context given by the
surrounding code determines what kind of data a particular <b>expression</b> is
expected to return. The three primary contexts are <b>list context</b>,
<b>scalar</b>, and <b>void context</b>. Scalar context is sometimes subdivided into
<b>Boolean context</b>, <b>numeric context</b>, <b>string context</b>, and <b>void
context</b>. There&#x2019;s also a &#x201c;don&#x2019;t care&#x201d; context (which is dealt with in Camel
chapter 2, &#x201c;Bits and Pieces&#x201d;, if you care).</p>
</li>
<li><a name="continuation"></a><b>continuation</b>
<p>The treatment of more than one physical <b>line</b> as a
single logical line. <b>Makefile</b> lines are continued by putting a backslash
before the <b>newline</b>. Mail headers, as defined by RFC 822, are
continued by putting a space or tab <i>after</i> the newline. In general, lines
in Perl do not need any form of continuation mark, because <b>whitespace</b>
(including newlines) is gleefully ignored. Usually.</p>
</li>
<li><a name="core-dump"></a><b>core dump</b>
<p>The corpse of a <b>process</b>, in the form of a file left in the
<b>working directory</b> of the process, usually as a result of certain kinds
of fatal errors.</p>
</li>
<li><a name="CPAN"></a><b>CPAN</b>
<p>The Comprehensive Perl Archive Network. (See the Camel Preface
and Camel chapter 19, &#x201c;CPAN&#x201d; for details.)</p>
</li>
<li><a name="C-preprocessor"></a><b>C preprocessor</b>
<p>The typical C compiler&#x2019;s first pass, which processes lines
beginning with <code class="inline"><span class="c">#</span></code>
 for conditional compilation and macro definition, and
does various manipulations of the program text based on the current
definitions. Also known as <i>cpp</i>(1).</p>
</li>
<li><a name="cracker"></a><b>cracker</b>
<p>Someone who breaks security on computer systems. A cracker may
be a true <b>hacker</b> or only a <b>script kiddie</b>.</p>
</li>
<li><a name="currently-selected-output-channel"></a><b>currently selected output channel</b>
<p>The last <b>filehandle</b> that was
designated with <code class="inline"><a class="l_k" href="functions/select.html">select(FILEHANDLE)</a></code>; <code class="inline"><span class="w">STDOUT</span></code>
, if no filehandle has
been selected.</p>
</li>
<li><a name="current-package"></a><b>current package</b>
<p>The <b>package</b> in which the current statement is
<b>compiled</b>. Scan backward in the text of your program through the current
<b>lexical scope</b> or any enclosing lexical scopes until you find a package
declaration. That&#x2019;s your current package name.</p>
</li>
<li><a name="current-working-directory"></a><b>current working directory</b>
<p>See <b>working directory</b>.</p>
</li>
<li><a name="CV"></a><b>CV</b>
<p>In academia, a curriculum vit&#xe6;, a fancy kind of r&#xe9;sum&#xe9;. In Perl, an internal &#x201c;code value&#x201d; typedef holding a
<b>subroutine</b>. The <code class="inline"><span class="w">CV</span></code>
 type is a subclass of <b>SV</b>.</p>
</li>
</ul>
<a name="D"></a><h2>D</h2>
<ul>
<li><a name="dangling-statement"></a><b>dangling statement</b>
<p>A bare, single <b>statement</b>,
without any braces, hanging off an <code class="inline">if</code>
 or <code class="inline">while</code>
 conditional. C allows
them. Perl doesn&#x2019;t.</p>
</li>
<li><a name="datagram"></a><b>datagram</b>
<p>A packet of data, such as a <b>UDP</b> message, that (from
the viewpoint of the programs involved) can be sent independently over the
network. (In fact, all packets are sent independently at the <b>IP</b> level,
but <b>stream</b> protocols such as <b>TCP</b> hide this from your program.)</p>
</li>
<li><a name="data-structure"></a><b>data structure</b>
<p>How your various pieces of data relate to each
other and what shape they make when you put them all together, as in a
rectangular table or a triangular tree.</p>
</li>
<li><a name="data-type"></a><b>data type</b>
<p>A set of possible values, together with all the
operations that know how to deal with those values. For example, a numeric
data type has a certain set of numbers that you can work with, as well as
various mathematical operations that you can do on the numbers, but would
make little sense on, say, a string such as <code class="inline"><span class="q">&quot;Kilroy&quot;</span></code>
. Strings have their
own operations, such as <b>concatenation</b>. Compound types made of a number of
smaller pieces generally have operations to compose and decompose them, and
perhaps to rearrange them. <b>Objects</b> that model things in the real world
often have operations that correspond to real activities. For instance, if
you model an elevator, your elevator object might have an <code class="inline"><span class="w">open_door</span></code>

<b>method</b>.</p>
</li>
<li><a name="DBM"></a><b>DBM</b>
<p>Stands for &#x201c;Database Management&#x201d; routines, a set of routines that emulate an
<b>associative array</b> using disk files. The routines use a dynamic hashing
scheme to locate any entry with only two disk accesses. DBM files allow a
Perl program to keep a persistent <b>hash</b> across multiple invocations. You
can <code class="inline"><a class="l_k" href="functions/tie.html">tie</a></code> your hash variables to various DBM implementations.</p>
</li>
<li><a name="declaration"></a><b>declaration</b>
<p>An <b>assertion</b> that states something exists and
perhaps describes what it&#x2019;s like, without giving any commitment as to how
or where you&#x2019;ll use it. A declaration is like the part of your recipe that
says, &#x201c;two cups flour, one large egg, four or five tadpoles&#x2026;&#x201d; See
<b>statement</b> for its opposite. Note that some declarations also function
as statements. Subroutine declarations also act as definitions if a body
is supplied.</p>
</li>
<li><a name="declarator"></a><b>declarator</b>
<p>Something that tells your program what sort of variable
you&#x2019;d like. Perl doesn&#x2019;t require you to declare variables, but you can use
<code class="inline"><a class="l_k" href="functions/my.html">my</a></code>, <code class="inline"><a class="l_k" href="functions/our.html">our</a></code>, or <code class="inline"><a class="l_k" href="functions/state.html">state</a></code> to denote that you want something other than
the default.</p>
</li>
<li><a name="decrement"></a><b>decrement</b>
<p>To subtract a value from a
variable, as in &#x201c;decrement <code class="inline"><span class="i">$x</span></code>
&#x201d; (meaning to remove 1 from its value) or
&#x201c;decrement <code class="inline"><span class="i">$x</span></code>
 by 3&#x201d;.</p>
</li>
<li><a name="default"></a><b>default</b>
<p>A <b>value</b> chosen for you if you don&#x2019;t
supply a value of your own.</p>
</li>
<li><a name="defined"></a><b>defined</b>
<p>Having a meaning. Perl thinks that some of the things
people try to do are devoid of meaning; in particular, making use of
variables that have never been given a <b>value</b> and performing certain
operations on data that isn&#x2019;t there. For example, if you try to read data
past the end of a file, Perl will hand you back an undefined value. See also
<b>false</b> and the <code class="inline"><a class="l_k" href="functions/defined.html">defined</a></code> entry in Camel chapter 27, &#x201c;Functions&#x201d;.</p>
</li>
<li><a name="delimiter"></a><b>delimiter</b>
<p>A <b>character</b> or <b>string</b> that sets bounds to an
arbitrarily sized textual object, not to be confused with a <b>separator</b> or
<b>terminator</b>. &#x201c;To delimit&#x201d; really just means &#x201c;to surround&#x201d; or &#x201c;to enclose&#x201d;
(like these parentheses are doing).</p>
</li>
<li><a name="dereference"></a><b>dereference</b>
<p>A fancy computer science term
meaning &#x201c;to follow a <b>reference</b> to what it points to&#x201d;. The &#x201c;de&#x201d; part of it
refers to the fact that you&#x2019;re taking away one level of <b>indirection</b>.</p>
</li>
<li><a name="derived-class"></a><b>derived class</b>
<p>A <b>class</b> that defines some of its <b>methods</b> in terms of a more generic class,
called a <b>base class</b>. Note that classes aren&#x2019;t classified exclusively into
base classes or derived classes: a class can function as both a derived
class and a base class simultaneously, which is kind of classy.</p>
</li>
<li><a name="descriptor"></a><b>descriptor</b>
<p>See <b>file descriptor</b>.</p>
</li>
<li><a name="destroy"></a><b>destroy</b>
<p>To deallocate the memory of a <b>referent</b> (first triggering
its <code class="inline">DESTROY</code>
 method, if it has one).</p>
</li>
<li><a name="destructor"></a><b>destructor</b>
<p>A special <b>method</b> that is called
when an <b>object</b> is thinking about <b>destroying</b> itself. A Perl program&#x2019;s
<code class="inline">DESTROY</code>
 method doesn&#x2019;t do the actual destruction; Perl just <b>triggers</b>
the method in case the <b>class</b> wants to do any associated cleanup.</p>
</li>
<li><a name="device"></a><b>device</b>
<p>A whiz-bang hardware gizmo (like a disk or tape drive or a
modem or a joystick or a mouse) attached to your computer, which the
<b>operating system</b> tries to make look like a <b>file</b> (or a bunch of files).
Under Unix, these fake files tend to live in the <i>/dev</i> directory.</p>
</li>
<li><a name="directive"></a><b>directive</b>
<p>A <b>pod</b> directive. See Camel chapter 23, &#x201c;Plain Old
Documentation&#x201d;.</p>
</li>
<li><a name="directory"></a><b>directory</b>
<p>A special file that contains other files. Some
<b>operating systems</b> call these &#x201c;folders&#x201d;, &#x201c;drawers&#x201d;, &#x201c;catalogues&#x201d;, or
&#x201c;catalogs&#x201d;.</p>
</li>
<li><a name="directory-handle"></a><b>directory handle</b>
<p>A name that represents a particular instance of opening a
directory to read it, until you close it. See the <code class="inline"><a class="l_k" href="functions/opendir.html">opendir</a></code> function.</p>
</li>
<li><a name="discipline"></a><b>discipline</b>
<p>Some people need this and some people avoid it.
For Perl, it&#x2019;s an old way to say <b>I/O layer</b>.</p>
</li>
<li><a name="dispatch"></a><b>dispatch</b>
<p>To send something to its correct destination. Often used
metaphorically to indicate a transfer of programmatic control to a
destination selected algorithmically, often by lookup in a table of function
<b>references</b> or, in the case of object <b>methods</b>, by traversing the
inheritance tree looking for the most specific definition for the method.</p>
</li>
<li><a name="distribution"></a><b>distribution</b>
<p>A standard, bundled release of a system of
software. The default usage implies source code is included. If that is not
the case, it will be called a &#x201c;binary-only&#x201d; distribution.</p>
</li>
<li><a name="dual-lived"></a><b>dual-lived</b>
<p>Some modules live both in the
<b>Standard Library</b> and on <b>CPAN</b>. These modules might be developed on two
tracks as people modify either version. The trend currently is to untangle
these situations.</p>
</li>
<li><a name="dweomer"></a><b>dweomer</b>
<p>An enchantment, illusion, phantasm, or jugglery. Said when Perl&#x2019;s
magical <b>dwimmer</b> effects don&#x2019;t do what you expect, but rather seem to be
the product of arcane <i>dweomercraft</i>, sorcery, or wonder working. [From
Middle English.]</p>
</li>
<li><a name="dwimmer"></a><b>dwimmer</b>
<p>DWIM is
an acronym for &#x201c;Do What I Mean&#x201d;, the principle that something
should just do what you want it to do without an undue amount of fuss. A bit
of code that does &#x201c;dwimming&#x201d; is a &#x201c;dwimmer&#x201d;. Dwimming can require a great
deal of behind-the-scenes magic, which (if it doesn&#x2019;t stay properly behind
the scenes) is called a <b>dweomer</b> instead.</p>
</li>
<li><a name="dynamic-scoping"></a><b>dynamic scoping</b>
<p>Dynamic scoping works over a <b>dynamic
scope</b>, making variables visible throughout the rest of the <b>block</b> in
which they are first used and in any <b>subroutines</b> that are called by the
rest of the block. Dynamically scoped variables can have their values
temporarily changed (and implicitly restored later) by a <code class="inline"><a class="l_k" href="functions/local.html">local</a></code> operator.
(Compare <b>lexical scoping</b>.) Used more loosely to mean how a subroutine
that is in the middle of calling another subroutine &#x201c;contains&#x201d; that
subroutine at <b>runtime</b>.</p>
</li>
</ul>
<a name="E"></a><h2>E</h2>
<ul>
<li><a name="eclectic"></a><b>eclectic</b>
<p>Derived from many sources. Some would say <i>too</i> many.</p>
</li>
<li><a name="element"></a><b>element</b>
<p>A basic building block. When you&#x2019;re talking about an
<b>array</b>, it&#x2019;s one of the items that make up the array.</p>
</li>
<li><a name="embedding"></a><b>embedding</b>
<p>When something is contained in something else,
particularly when that might be considered surprising: &#x201c;I&#x2019;ve embedded a
complete Perl interpreter in my editor!&#x201d;</p>
</li>
<li><a name="empty-subclass-test"></a><b>empty subclass test</b>
<p>The notion that an empty <b>derived class</b> should
behave exactly like its <b>base class</b>.</p>
</li>
<li><a name="encapsulation"></a><b>encapsulation</b>
<p>The veil of abstraction separating the <b>interface</b>
from the <b>implementation</b> (whether enforced or not), which mandates that
all access to an <b>object</b>&#x2019;s state be through <b>methods</b> alone.</p>
</li>
<li><a name="endian"></a><b>endian</b>
<p>See <b>little-endian</b> and <b>big-endian</b>.</p>
</li>
<li><a name="en-passant"></a><b>en passant</b>
<p>When you change a <b>value</b> as it is being copied. [From
French &#x201c;in passing&#x201d;, as in the exotic pawn-capturing maneuver in chess.]</p>
</li>
<li><a name="environment"></a><b>environment</b>
<p>The collective set of <b>environment variables</b> your
<b>process</b> inherits from its parent. Accessed via <code class="inline"><span class="i">%ENV</span></code>
.</p>
</li>
<li><a name="environment-variable"></a><b>environment variable</b>
<p>A mechanism by which some high-level agent such as a user can pass its
preferences down to its future offspring (child <b>processes</b>, grandchild
processes, great-grandchild processes, and so on). Each environment
variable is a <b>key</b>/<b>value</b> pair, like one entry in a <b>hash</b>.</p>
</li>
<li><a name="EOF"></a><b>EOF</b>
<p>End of File. Sometimes used
metaphorically as the terminating string of a <b>here document</b>.</p>
</li>
<li><a name="errno"></a><b>errno</b>
<p>The error number returned by a
<b>syscall</b> when it fails. Perl refers to the error by the name <code class="inline"><span class="i">$!</span></code>
 (or
<code class="inline"><span class="i">$OS_ERROR</span></code>
 if you use the English module).</p>
</li>
<li><a name="error"></a><b>error</b>
<p>See <b>exception</b> or <b>fatal error</b>.</p>
</li>
<li><a name="escape-sequence"></a><b>escape sequence</b>
<p>See <b>metasymbol</b>.</p>
</li>
<li><a name="exception"></a><b>exception</b>
<p>A fancy term for an error. See <b>fatal error</b>.</p>
</li>
<li><a name="exception-handling"></a><b>exception handling</b>
<p>The way a program responds to an error. The
exception-handling mechanism in Perl is the <code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code> operator.</p>
</li>
<li><a name="exec"></a><b>exec</b>
<p>To throw away the current <b>process</b>&#x2019;s program and replace
it with another, without exiting the process or relinquishing any resources
held (apart from the old memory image).</p>
</li>
<li><a name="executable-file"></a><b>executable file</b>
<p>A <b>file</b> that is specially marked to
tell the <b>operating system</b> that it&#x2019;s okay to run this file as a program.
Usually shortened to &#x201c;executable&#x201d;.</p>
</li>
<li><a name="execute"></a><b>execute</b>
<p>To run a <b>program</b> or <b>subroutine</b>. (Has nothing to do
with the <code class="inline"><a class="l_k" href="functions/kill.html">kill</a></code> built-in, unless you&#x2019;re trying to run a <b>signal handler</b>.)</p>
</li>
<li><a name="execute-bit"></a><b>execute bit</b>
<p>The special mark that tells the operating system it can run
this program. There are actually three execute bits under Unix, and which
bit gets used depends on whether you own the file singularly, collectively,
or not at all.</p>
</li>
<li><a name="exit-status"></a><b>exit status</b>
<p>See <b>status</b>.</p>
</li>
<li><a name="exploit"></a><b>exploit</b>
<p>Used as a noun in this case, this refers to a known way
to compromise a program to get it to do something the author didn&#x2019;t intend.
Your task is to write unexploitable programs.</p>
</li>
<li><a name="export"></a><b>export</b>
<p>To make symbols from a <b>module</b> available for
<b>import</b> by other modules.</p>
</li>
<li><a name="expression"></a><b>expression</b>
<p>Anything you can legally say in a spot
where a <b>value</b> is required. Typically composed of <b>literals</b>,
<b>variables</b>, <b>operators</b>, <b>functions</b>, and <b>subroutine</b> calls, not
necessarily in that order.</p>
</li>
<li><a name="extension"></a><b>extension</b>
<p>A Perl module that also pulls in <b>compiled</b> C or C++
code. More generally, any experimental option that can be <b>compiled</b> into
Perl, such as multithreading.</p>
</li>
</ul>
<a name="F"></a><h2>F</h2>
<ul>
<li><a name="false"></a><b>false</b>
<p>In Perl, any value that would look like <code class="inline"><span class="q">&quot;&quot;</span></code>

or <code class="inline"><span class="q">&quot;0&quot;</span></code>
 if evaluated in a string context. Since undefined values evaluate
to <code class="inline"><span class="q">&quot;&quot;</span></code>
, all undefined values are false, but not all false values are
undefined.</p>
</li>
<li><a name="FAQ"></a><b>FAQ</b>
<p>Frequently Asked Question (although not necessarily
frequently answered, especially if the answer appears in the Perl FAQ
shipped standard with Perl).</p>
</li>
<li><a name="fatal-error"></a><b>fatal error</b>
<p>An uncaught <b>exception</b>, which causes termination of the
<b>process</b> after printing a message on your <b>standard error</b> stream. Errors
that happen inside an <code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code> are not fatal. Instead, the <code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code> terminates
after placing the exception message in the <code class="inline"><span class="i">$@</span></code>
 (<code class="inline"><span class="i">$EVAL_ERROR</span></code>
) variable.
You can try to provoke a fatal error with the <code class="inline"><a class="l_k" href="functions/die.html">die</a></code> operator (known as
throwing or raising an exception), but this may be caught by a dynamically
enclosing <code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code>. If not caught, the <code class="inline"><a class="l_k" href="functions/die.html">die</a></code> becomes a fatal error.</p>
</li>
<li><a name="feeping-creaturism"></a><b>feeping creaturism</b>
<p>A spoonerism of &#x201c;creeping
featurism&#x201d;, noting the biological urge to add just one more feature to
a program.</p>
</li>
<li><a name="field"></a><b>field</b>
<p>A single piece of numeric or string data that is part of a
longer <b>string</b>, <b>record</b>, or <b>line</b>. Variable-width fields are usually
split up by <b>separators</b> (so use <code class="inline"><a class="l_k" href="functions/split.html">split</a></code> to extract the fields), while
fixed-width fields are usually at fixed positions (so use <code class="inline"><a class="l_k" href="functions/unpack.html">unpack</a></code>).
<b>Instance variables</b> are also known as &#x201c;fields&#x201d;.</p>
</li>
<li><a name="FIFO"></a><b>FIFO</b>
<p>First In, First Out. See also <b>LIFO</b>. Also a nickname for a <b>named pipe</b>.</p>
</li>
<li><a name="file"></a><b>file</b>
<p>A named collection of data, usually stored on disk in a
<b>directory</b> in a <b>filesystem</b>. Roughly like a document, if you&#x2019;re into
office metaphors. In modern filesystems, you can actually give a file more
than one name. Some files have special properties, like directories and
devices.</p>
</li>
<li><a name="file-descriptor"></a><b>file descriptor</b>
<p>The little number the <b>operating
system</b> uses to keep track of which opened <b>file</b> you&#x2019;re talking about.
Perl hides the file descriptor inside a <b>standard I/O</b> stream and then
attaches the stream to a <b>filehandle</b>.</p>
</li>
<li><a name="fileglob"></a><b>fileglob</b>
<p>A &#x201c;wildcard&#x201d; match on <b>filenames</b>. See the <code class="inline"><a class="l_k" href="functions/glob.html">glob</a></code> function.</p>
</li>
<li><a name="filehandle"></a><b>filehandle</b>
<p>An identifier (not necessarily related to the real
name of a file) that represents a particular instance of opening a file,
until you close it. If you&#x2019;re going to open and close several different
files in succession, it&#x2019;s fine to open each of them with the same
filehandle, so you don&#x2019;t have to write out separate code to process each
file.</p>
</li>
<li><a name="filename"></a><b>filename</b>
<p>One name for a file. This name is listed in a
<b>directory</b>. You can use it in an <code class="inline"><a class="l_k" href="functions/open.html">open</a></code> to tell the <b>operating system</b>
exactly which file you want to open, and associate the file with a
<b>filehandle</b>, which will carry the subsequent identity of that file in
your program, until you close it.</p>
</li>
<li><a name="filesystem"></a><b>filesystem</b>
<p>A set of <b>directories</b> and <b>files</b> residing on a
partition of the disk. Sometimes known as a &#x201c;partition&#x201d;. You can change the
file&#x2019;s name or even move a file around from directory to directory within a
filesystem without actually moving the file itself, at least under Unix.</p>
</li>
<li><a name="file-test-operator"></a><b>file test operator</b>
<p>A built-in unary operator that you use to
determine whether something is <b>true</b> about a file, such as <code class="inline"><span class="q">&ndash;o</span>
<span class="q">$filename</span></code>
 to test whether you&#x2019;re the owner of the file.</p>
</li>
<li><a name="filter"></a><b>filter</b>
<p>A program designed to take a <b>stream</b> of input and
transform it into a stream of output.</p>
</li>
<li><a name="first-come"></a><b>first-come</b>
<p>The first <b>PAUSE</b>
author to upload a <b>namespace</b> automatically becomes the <b>primary
maintainer</b> for that namespace. The &#x201c;first come&#x201d; permissions distinguish a
<b>primary maintainer</b> who was assigned that role from one who received it
automatically.</p>
</li>
<li><a name="flag"></a><b>flag</b>
<p>We tend to avoid this term because it means so many things.
It may mean a command-line <b>switch</b> that takes no argument itself (such as
Perl&#x2019;s <code class="inline"><span class="q">&ndash;n</span></code>
 and <code class="inline"><span class="q">&ndash;p</span></code>
 flags) or, less frequently, a single-bit indicator
(such as the <code class="inline"><span class="w">O_CREAT</span></code>
 and <code class="inline"><span class="w">O_EXCL</span></code>
 flags used in <code class="inline"><a class="l_k" href="functions/sysopen.html">sysopen</a></code>). Sometimes
informally used to refer to certain regex modifiers.</p>
</li>
<li><a name="floating-point"></a><b>floating point</b>
<p>A method of storing
numbers in &#x201c;scientific notation&#x201d;, such that the precision of the number is
independent of its magnitude (the decimal point &#x201c;floats&#x201d;). Perl does its
numeric work with floating-point numbers (sometimes called &#x201c;floats&#x201d;) when
it can&#x2019;t get away with using <b>integers</b>. Floating-point numbers are mere
approximations of real numbers.</p>
</li>
<li><a name="flush"></a><b>flush</b>
<p>The act of emptying a <b>buffer</b>,
often before it&#x2019;s full.</p>
</li>
<li><a name="FMTEYEWTK"></a><b>FMTEYEWTK</b>
<p>Far More Than Everything You Ever Wanted To Know. An
exhaustive treatise on one narrow topic, something of a super-<b>FAQ</b>. See
Tom for far more.</p>
</li>
<li><a name="foldcase"></a><b>foldcase</b>
<p>The casemap used in Unicode when comparing or matching
without regard to case. Comparing lower-, title-, or uppercase are all
unreliable due to Unicode&#x2019;s complex, one-to-many case mappings. Foldcase is
a <b>lowercase</b> variant (using a partially decomposed <b>normalization</b> form
for certain codepoints) created specifically to resolve this.</p>
</li>
<li><a name="fork"></a><b>fork</b>
<p>To create a child <b>process</b>
identical to the parent process at its moment of conception, at least until
it gets ideas of its own. A thread with protected memory.</p>
</li>
<li><a name="formal-arguments"></a><b>formal arguments</b>
<p>The generic names by which a
<b>subroutine</b> knows its <b>arguments</b>. In many languages, formal arguments
are always given individual names; in Perl, the formal arguments are just
the elements of an array. The formal arguments to a Perl program are
<code class="inline"><span class="i">$ARGV</span>[<span class="n">0</span>]</code>
, <code class="inline"><span class="i">$ARGV</span>[<span class="n">1</span>]</code>
, and so on. Similarly, the formal arguments to a
Perl subroutine are <code class="inline"><span class="i">$_</span>[<span class="n">0</span>]</code>
, <code class="inline"><span class="i">$_</span>[<span class="n">1</span>]</code>
, and so on. You may give the
arguments individual names by assigning the values to a <code class="inline"><a class="l_k" href="functions/my.html">my</a></code> list. See
also <b>actual arguments</b>.</p>
</li>
<li><a name="format"></a><b>format</b>
<p>A specification of how many spaces and digits and things
to put somewhere so that whatever you&#x2019;re printing comes out nice and
pretty.</p>
</li>
<li><a name="freely-available"></a><b>freely available</b>
<p>Means you don&#x2019;t have to pay money to get it, but
the copyright on it may still belong to someone else (like Larry).</p>
</li>
<li><a name="freely-redistributable"></a><b>freely redistributable</b>
<p>Means you&#x2019;re not in legal trouble if you
give a bootleg copy of it to your friends and we find out about it. In
fact, we&#x2019;d rather you gave a copy to all your friends.</p>
</li>
<li><a name="freeware"></a><b>freeware</b>
<p>Historically, any software that you give away,
particularly if you make the source code available as well. Now often
called <b>open source software</b>. Recently there has been a trend to use the
term in contradistinction to <b>open source software</b>, to refer only to free
software released under the Free Software
Foundation&#x2019;s GPL (General Public License), but this is difficult to justify
etymologically.</p>
</li>
<li><a name="function"></a><b>function</b>
<p>Mathematically, a mapping of each of a set of input
values to a particular output value. In computers, refers to a
<b>subroutine</b> or <b>operator</b> that returns a <b>value</b>. It may or may not
have input values (called <b>arguments</b>).</p>
</li>
<li><a name="funny-character"></a><b>funny character</b>
<p>Someone like Larry, or one of his
peculiar friends. Also refers to the strange prefixes that Perl requires as
noun markers on its variables.</p>
</li>
</ul>
<a name="G"></a><h2>G</h2>
<ul>
<li><a name="garbage-collection"></a><b>garbage collection</b>
<p>A misnamed feature&#x2014;it should be called,
&#x201c;expecting your mother to pick up after you&#x201d;. Strictly speaking, Perl
doesn&#x2019;t do this, but it relies on a reference-counting mechanism to keep
things tidy. However, we rarely speak strictly and will often refer to the
reference-counting scheme as a form of garbage collection. (If it&#x2019;s any
comfort, when your interpreter exits, a &#x201c;real&#x201d; garbage collector runs to
make sure everything is cleaned up if you&#x2019;ve been messy with circular
references and such.)</p>
</li>
<li><a name="GID"></a><b>GID</b>
<p>Group ID&#x2014;in Unix, the numeric group ID
that the <b>operating system</b> uses to identify you and members of your
<b>group</b>.</p>
</li>
<li><a name="glob"></a><b>glob</b>
<p>Strictly, the shell&#x2019;s <code class="inline"><span class="i">*</span></code>
 character, which will match
a &#x201c;glob&#x201d; of characters when you&#x2019;re trying to generate a list of filenames.
Loosely, the act of using globs and similar symbols to do pattern matching.
See also <b>fileglob</b> and <b>typeglob</b>.</p>
</li>
<li><a name="global"></a><b>global</b>
<p>Something you can see from anywhere, usually used of
<b>variables</b> and <b>subroutines</b> that are visible everywhere in your
program.  In Perl, only certain special variables are truly global&#x2014;most
variables (and all subroutines) exist only in the current <b>package</b>.
Global variables can be declared with <code class="inline"><a class="l_k" href="functions/our.html">our</a></code>. See &#x201c;Global Declarations&#x201d; in
Camel chapter 4, &#x201c;Statements and Declarations&#x201d;.</p>
</li>
<li><a name="global-destruction"></a><b>global destruction</b>
<p>The <b>garbage collection</b> of globals (and the running
of any associated object destructors) that takes place when a Perl
<b>interpreter</b> is being shut down. Global destruction should not be
confused with the Apocalypse, except perhaps when it should.</p>
</li>
<li><a name="glue-language"></a><b>glue language</b>
<p>A language such as Perl that is good at hooking things
together that weren&#x2019;t intended to be hooked together.</p>
</li>
<li><a name="granularity"></a><b>granularity</b>
<p>The size of the pieces you&#x2019;re dealing with, mentally
speaking.</p>
</li>
<li><a name="grapheme"></a><b>grapheme</b>
<p>A graphene is an allotrope of carbon arranged in a
hexagonal crystal lattice one atom thick. A <b>grapheme</b>, or more fully, a
<i>grapheme cluster string</i> is a single user-visible <b>character</b>, which may
in turn be several characters (<b>codepoints</b>) long. For example, a carriage
return plus a line feed is a single grapheme but two characters, while a
&#x201c;&#x22b;&#x201d; is a single grapheme but one, two, or even three characters, depending
on <b>normalization</b>.</p>
</li>
<li><a name="greedy"></a><b>greedy</b>
<p>A <b>subpattern</b> whose
<b>quantifier</b> wants to match as many things as possible.</p>
</li>
<li><a name="grep"></a><b>grep</b>
<p>Originally from the old Unix editor command for &#x201c;Globally
search for a Regular Expression and Print it&#x201d;, now used in the general
sense of any kind of search, especially text searches. Perl has a built-in
<code class="inline"><a class="l_k" href="functions/grep.html">grep</a></code> function that searches a list for elements matching any given
criterion, whereas the <b>grep</b>(1) program searches for lines matching a
<b>regular expression</b> in one or more files.</p>
</li>
<li><a name="group"></a><b>group</b>
<p>A set of users of which you are a member. In some
operating systems (like Unix), you can give certain file access permissions
to other members of your group.</p>
</li>
<li><a name="GV"></a><b>GV</b>
<p>An internal &#x201c;glob value&#x201d; typedef,
holding a <b>typeglob</b>. The <code class="inline"><span class="w">GV</span></code>
 type is a subclass of <b>SV</b>.</p>
</li>
</ul>
<a name="H"></a><h2>H</h2>
<ul>
<li><a name="hacker"></a><b>hacker</b>
<p>Someone who is brilliantly persistent in solving technical
problems, whether these involve golfing, fighting orcs, or programming.
Hacker is a neutral term, morally speaking. Good hackers are not to be
confused with evil <b>crackers</b> or clueless <b>script kiddies</b>. If you
confuse them, we will presume that you are either evil or clueless.</p>
</li>
<li><a name="handler"></a><b>handler</b>
<p>A <b>subroutine</b> or <b>method</b> that Perl calls when your
program needs to respond to some internal event, such as a <b>signal</b>, or an
encounter with an operator subject to <b>operator overloading</b>. See also
<b>callback</b>.</p>
</li>
<li><a name="hard-reference"></a><b>hard reference</b>
<p>A <b>scalar</b> <b>value</b> containing
the actual address of a <b>referent</b>, such that the referent&#x2019;s <b>reference</b>
count accounts for it. (Some hard references are held internally, such as
the implicit reference from one of a <b>typeglob</b>&#x2019;s variable slots to its
corresponding referent.) A hard reference is different from a <b>symbolic
reference</b>.</p>
</li>
<li><a name="hash"></a><b>hash</b>
<p>An unordered association of <b>key</b>/<b>value</b> pairs, stored such that you can easily use a string <b>key</b> to
look up its associated data <b>value</b>. This glossary is like a hash, where
the word to be defined is the key and the definition is the value. A hash
is also sometimes septisyllabically called an &#x201c;associative array&#x201d;, which is
a pretty good reason for simply calling it a &#x201c;hash&#x201d; instead.</p>
</li>
<li><a name="hash-table"></a><b>hash table</b>
<p>A data structure used internally by Perl for implementing
associative arrays (hashes) efficiently. See also <b>bucket</b>.</p>
</li>
<li><a name="header-file"></a><b>header file</b>
<p>A file containing certain required
definitions that you must include &#x201c;ahead&#x201d; of the rest of your program to do
certain obscure operations. A C header file has a <i>.h</i> extension. Perl
doesn&#x2019;t really have header files, though historically Perl has sometimes
used translated <i>.h</i> files with a <i>.ph</i> extension. See <code class="inline"><a class="l_k" href="functions/require.html">require</a></code> in
Camel chapter 27, &#x201c;Functions&#x201d;. (Header files have been superseded by the
<b>module</b> mechanism.)</p>
</li>
<li><a name="here-document"></a><b>here document</b>
<p>So called because of a similar construct in <b>shells</b> that
pretends that the <b>lines</b> following the <b>command</b> are a separate <b>file</b>
to be fed to the command, up to some terminating string. In Perl, however,
it&#x2019;s just a fancy form of quoting.</p>
</li>
<li><a name="hexadecimal"></a><b>hexadecimal</b>
<p>A number in base 16, &#x201c;hex&#x201d; for short. The digits for 10
through 15 are customarily represented by the letters <code class="inline"><span class="w">a</span></code>
 through <code class="inline"><span class="w">f</span></code>
.
Hexadecimal constants in Perl start with <code class="inline"><span class="n">0</span>x</code>
. See also the <code class="inline"><a class="l_k" href="functions/hex.html">hex</a></code>
function in Camel chapter 27, &#x201c;Functions&#x201d;.</p>
</li>
<li><a name="home-directory"></a><b>home directory</b>
<p>The directory you are put into when
you log in. On a Unix system, the name is often placed into <code class="inline"><span class="i">$ENV</span>{<span class="w">HOME</span>}</code>

or <code class="inline"><span class="i">$ENV</span>{<span class="w">LOGDIR</span>}</code>
 by <i>login</i>, but you can also find it with
<code class="inline"><span class="s">(</span><span class="w">get</span></code>
<code class="inline"><span class="i">pwuid</span><span class="s">(</span><span class="i">$&lt;</span><span class="s">)</span><span class="p">)</span>[<span class="n">7</span>]</code>
. (Some platforms do not have a concept of a
home directory.)</p>
</li>
<li><a name="host"></a><b>host</b>
<p>The computer on which a program or other data resides.</p>
</li>
<li><a name="hubris"></a><b>hubris</b>
<p>Excessive pride, the sort of thing for which Zeus zaps
you.  Also the quality that makes you write (and maintain) programs that
other people won&#x2019;t want to say bad things about. Hence, the third great
virtue of a programmer. See also <b>laziness</b> and <b>impatience</b>.</p>
</li>
<li><a name="HV"></a><b>HV</b>
<p>Short for a &#x201c;hash value&#x201d; typedef, which
holds Perl&#x2019;s internal representation of a hash. The <code class="inline"><span class="w">HV</span></code>
 type is a
subclass of <b>SV</b>.</p>
</li>
</ul>
<a name="I"></a><h2>I</h2>
<ul>
<li><a name="identifier"></a><b>identifier</b>
<p>A legally formed name for most anything in which a
computer program might be interested. Many languages (including Perl) allow
identifiers to start with an alphabetic character, and then contain
alphabetics and digits. Perl also allows connector punctuation like the
underscore character wherever it allows alphabetics. (Perl also has more
complicated names, like <b>qualified</b> names.)</p>
</li>
<li><a name="impatience"></a><b>impatience</b>
<p>The anger you feel when the computer is being lazy.
This makes you write programs that don&#x2019;t just react to your needs, but
actually anticipate them. Or at least that pretend to. Hence, the second
great virtue of a programmer. See also <b>laziness</b> and <b>hubris</b>.</p>
</li>
<li><a name="implementation"></a><b>implementation</b>
<p>How a piece of code actually goes about doing its
job. Users of the code should not count on implementation details staying
the same unless they are part of the published <b>interface</b>.</p>
</li>
<li><a name="import"></a><b>import</b>
<p>To gain access to symbols that are exported from another
module. See <code class="inline"><a class="l_k" href="functions/use.html">use</a></code> in Camel chapter 27, &#x201c;Functions&#x201d;.</p>
</li>
<li><a name="increment"></a><b>increment</b>
<p>To increase the value of
something by 1 (or by some other number, if so specified).</p>
</li>
<li><a name="indexing"></a><b>indexing</b>
<p>In olden days, the act of looking up a <b>key</b> in an
actual index (such as a phone book). But now it's merely the act of using
any kind of key or position to find the corresponding <b>value</b>, even if no
index is involved. Things have degenerated to the point that Perl&#x2019;s
<code class="inline"><a class="l_k" href="functions/index.html">index</a></code> function merely locates the position (index) of one string in
another.</p>
</li>
<li><a name="indirect-filehandle"></a><b>indirect filehandle</b>
<p>An <b>expression</b> that
evaluates to something that can be used as a <b>filehandle</b>: a <b>string</b>
(filehandle name), a <b>typeglob</b>, a typeglob <b>reference</b>, or a low-level
<b>IO</b> object.</p>
</li>
<li><a name="indirection"></a><b>indirection</b>
<p>If something in a program isn&#x2019;t the value you&#x2019;re
looking for but indicates where the value is, that&#x2019;s indirection. This can
be done with either <b>symbolic references</b> or <b>hard</b>.</p>
</li>
<li><a name="indirect-object"></a><b>indirect object</b>
<p>In English grammar, a short
noun phrase between a verb and its direct object indicating the beneficiary
or recipient of the action. In Perl, <code class="inline"><a class="l_k" href="functions/print.html">print</a> <span class="i">STDOUT</span> <span class="q">&quot;$foo\n&quot;</span><span class="sc">;</span></code>
 can be
understood as &#x201c;verb indirect-object object&#x201d;, where <code class="inline"><span class="w">STDOUT</span></code>
 is the
recipient of the <code class="inline"><a class="l_k" href="functions/print.html">print</a></code> action, and <code class="inline"><span class="q">&quot;$foo&quot;</span></code>
 is the object being
printed.  Similarly, when invoking a <b>method</b>, you might place the
invocant in the dative slot between the method and its arguments:</p>
<pre class="verbatim"><ol><li>    <span class="i">$gollum</span> = <span class="w">new</span> <span class="w">Pathetic::Creature</span> <span class="q">&quot;Sm&eacute;agol&quot;</span><span class="sc">;</span></li><li>    <span class="w">give</span> <span class="i">$gollum</span> <span class="q">&quot;Fisssssh!&quot;</span><span class="sc">;</span></li><li>    <span class="w">give</span> <span class="i">$gollum</span> <span class="q">&quot;Precious!&quot;</span><span class="sc">;</span></li></ol></pre></li>
<li><a name="indirect-object-slot"></a><b>indirect object slot</b>
<p>The syntactic position falling between a method call
and its arguments when using the indirect object invocation syntax. (The
slot is distinguished by the absence of a comma between it and the next
argument.) <code class="inline"><span class="w">STDERR</span></code>
 is in the indirect object slot here:</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/print.html">print</a> <span class="i">STDERR</span> <span class="q">&quot;Awake! Awake! Fear, Fire, Foes! Awake!\n&quot;</span><span class="sc">;</span></li></ol></pre></li>
<li><a name="infix"></a><b>infix</b>
<p>An <b>operator</b> that comes in between its <b>operands</b>,
such as multiplication in <code class="inline"><span class="n">24</span> * <span class="n">7</span></code>
.</p>
</li>
<li><a name="inheritance"></a><b>inheritance</b>
<p>What you get from your ancestors, genetically or
otherwise. If you happen to be a <b>class</b>, your ancestors are called <b>base
classes</b> and your descendants are called <b>derived classes</b>. See <b>single
inheritance</b> and <b>multiple inheritance</b>.</p>
</li>
<li><a name="instance"></a><b>instance</b>
<p>Short for &#x201c;an instance of a class&#x201d;, meaning an <b>object</b>
of that <b>class</b>.</p>
</li>
<li><a name="instance-data"></a><b>instance data</b>
<p>See <b>instance variable</b>.</p>
</li>
<li><a name="instance-method"></a><b>instance method</b>
<p>A <b>method</b> of an <b>object</b>, as
opposed to a <b>class method</b>.</p>
<p>A <b>method</b> whose <b>invocant</b> is an <b>object</b>, not a <b>package</b> name. Every
object of a class shares all the methods of that class, so an instance
method applies to all instances of the class, rather than applying to a
particular instance. Also see <b>class method</b>.</p>
</li>
<li><a name="instance-variable"></a><b>instance variable</b>
<p>An <b>attribute</b> of an <b>object</b>; data stored with the particular object rather than with the class
as a whole.</p>
</li>
<li><a name="integer"></a><b>integer</b>
<p>A number with no fractional (decimal) part. A counting
number, like 1, 2, 3, and so on, but including 0 and the negatives.</p>
</li>
<li><a name="interface"></a><b>interface</b>
<p>The services a piece of code promises to provide
forever, in contrast to its <b>implementation</b>, which it should feel free to
change whenever it likes.</p>
</li>
<li><a name="interpolation"></a><b>interpolation</b>
<p>The insertion of a scalar or list value somewhere
in the middle of another value, such that it appears to have been there all
along. In Perl, variable interpolation happens in double-quoted strings and
patterns, and list interpolation occurs when constructing the list of
values to pass to a list operator or other such construct that takes a
<i><code class="inline"><span class="w">LIST</span></code>
</i>.</p>
</li>
<li><a name="interpreter"></a><b>interpreter</b>
<p>Strictly speaking, a program that reads a second
program and does what the second program says directly without turning the
program into a different form first, which is what <b>compilers</b> do. Perl is
not an interpreter by this definition, because it contains a kind of
compiler that takes a program and turns it into a more executable form
(<b>syntax trees</b>) within the <i>perl</i> process itself, which the Perl
<b>runtime</b> system then interprets.</p>
</li>
<li><a name="invocant"></a><b>invocant</b>
<p>The agent on whose behalf a <b>method</b> is invoked. In a
<b>class</b> method, the invocant is a package name. In an <b>instance</b> method,
the invocant is an object reference.</p>
</li>
<li><a name="invocation"></a><b>invocation</b>
<p>The act of calling up a deity, daemon, program,
method, subroutine, or function to get it to do what you think it&#x2019;s
supposed to do.  We usually &#x201c;call&#x201d; subroutines but &#x201c;invoke&#x201d; methods, since
it sounds cooler.</p>
</li>
<li><a name="I%2fO"></a><b>I/O</b>
<p>Input from, or output to, a <b>file</b> or <b>device</b>.</p>
</li>
<li><a name="IO"></a><b>IO</b>
<p>An internal I/O object. Can also mean <b>indirect object</b>.</p>
</li>
<li><a name="I%2fO-layer"></a><b>I/O layer</b>
<p>One of the filters between the data and what you get as input
or what you end up with as output.</p>
</li>
<li><a name="IPA"></a><b>IPA</b>
<p>India Pale Ale. Also the International Phonetic Alphabet, the
standard alphabet used for phonetic notation worldwide. Draws heavily on
Unicode, including many combining characters.</p>
</li>
<li><a name="IP"></a><b>IP</b>
<p>Internet Protocol, or
Intellectual
Property.</p>
</li>
<li><a name="IPC"></a><b>IPC</b>
<p>Interprocess Communication.</p>
</li>
<li><a name="is-a"></a><b>is-a</b>
<p>A relationship between two <b>objects</b> in which one
object is considered to be a more specific version of the other, generic
object: &#x201c;A camel is a mammal.&#x201d; Since the generic object really only exists
in a Platonic sense, we usually add a little abstraction to the notion of
objects and think of the relationship as being between a generic <b>base
class</b> and a specific <b>derived class</b>. Oddly enough, Platonic classes
don&#x2019;t always have Platonic relationships&#x2014;see <b>inheritance</b>.</p>
</li>
<li><a name="iteration"></a><b>iteration</b>
<p>Doing something repeatedly.</p>
</li>
<li><a name="iterator"></a><b>iterator</b>
<p>A special programming gizmo that keeps track of where you are
in something that you&#x2019;re trying to iterate over. The <code class="inline">foreach</code>
 loop in
Perl contains an iterator; so does a hash, allowing you to <code class="inline"><a class="l_k" href="functions/each.html">each</a></code> through
it.</p>
</li>
<li><a name="IV"></a><b>IV</b>
<p>The integer four, not to be
confused with six, Tom&#x2019;s favorite editor. IV also means an internal Integer
Value of the type a <b>scalar</b> can hold, not to be confused with an <b>NV</b>.</p>
</li>
</ul>
<a name="J"></a><h2>J</h2>
<ul>
<li><a name="JAPH"></a><b>JAPH</b>
<p>&#x201c;Just Another Perl Hacker&#x201d;, a clever but cryptic bit of Perl
code that, when executed, evaluates to that string. Often used to
illustrate a particular Perl feature, and something of an ongoing
Obfuscated Perl Contest seen in USENET signatures.</p>
</li>
</ul>
<a name="K"></a><h2>K</h2>
<ul>
<li><a name="key"></a><b>key</b>
<p>The string index to a <b>hash</b>, used to look up the <b>value</b>
associated with that key.</p>
</li>
<li><a name="keyword"></a><b>keyword</b>
<p>See <b>reserved words</b>.</p>
</li>
</ul>
<a name="L"></a><h2>L</h2>
<ul>
<li><a name="label"></a><b>label</b>
<p>A name you give to a <b>statement</b> so that you can talk
about that statement elsewhere in the program.</p>
</li>
<li><a name="laziness"></a><b>laziness</b>
<p>The quality that makes you go to great effort to reduce
overall energy expenditure. It makes you write labor-saving programs that
other people will find useful, and then document what you wrote so you
don&#x2019;t have to answer so many questions about it. Hence, the first great
virtue of a programmer. Also hence, this book. See also <b>impatience</b> and
<b>hubris</b>.</p>
</li>
<li><a name="leftmost-longest"></a><b>leftmost longest</b>
<p>The preference of the <b>regular expression</b> engine to match the
leftmost occurrence of a <b>pattern</b>, then given a position at which a match
will occur, the preference for the longest match (presuming the use of a
<b>greedy</b> quantifier). See Camel chapter 5, &#x201c;Pattern Matching&#x201d; for <i>much</i>
more on this subject.</p>
</li>
<li><a name="left-shift"></a><b>left shift</b>
<p>A <b>bit shift</b> that multiplies the
number by some power of 2.</p>
</li>
<li><a name="lexeme"></a><b>lexeme</b>
<p>Fancy term for a <b>token</b>.</p>
</li>
<li><a name="lexer"></a><b>lexer</b>
<p>Fancy term for a <b>tokener</b>.</p>
</li>
<li><a name="lexical-analysis"></a><b>lexical analysis</b>
<p>Fancy term for <b>tokenizing</b>.</p>
</li>
<li><a name="lexical-scoping"></a><b>lexical scoping</b>
<p>Looking at your <i>Oxford English
Dictionary</i> through a microscope. (Also known as <b>static scoping</b>, because
dictionaries don&#x2019;t change very fast.) Similarly, looking at variables
stored in a private dictionary (namespace) for each scope, which are
visible only from their point of declaration down to the end of the lexical scope in which they are declared. &#x2014;Syn.
<b>static scoping</b>. &#x2014;Ant. <b>dynamic scoping</b>.</p>
</li>
<li><a name="lexical-variable"></a><b>lexical variable</b>
<p>A <b>variable</b> subject to
<b>lexical scoping</b>, declared by <code class="inline"><a class="l_k" href="functions/my.html">my</a></code>. Often just called a &#x201c;lexical&#x201d;. (The
<code class="inline"><a class="l_k" href="functions/our.html">our</a></code> declaration declares a lexically scoped name for a global variable,
which is not itself a lexical variable.)</p>
</li>
<li><a name="library"></a><b>library</b>
<p>Generally, a collection of procedures. In ancient
days, referred to a collection of subroutines in a <i>.pl</i> file. In modern
times, refers more often to the entire collection of Perl <b>modules</b> on
your system.</p>
</li>
<li><a name="LIFO"></a><b>LIFO</b>
<p>Last In, First Out. See also <b>FIFO</b>. A LIFO is usually called a
<b>stack</b>.</p>
</li>
<li><a name="line"></a><b>line</b>
<p>In Unix, a sequence of zero or more nonnewline characters
terminated with a <b>newline</b> character. On non-Unix machines, this is
emulated by the C library even if the underlying <b>operating system</b> has
different ideas.</p>
</li>
<li><a name="linebreak"></a><b>linebreak</b>
<p>A <b>grapheme</b> consisting of either a carriage return followed
by a line feed or any character with the Unicode Vertical Space <b>character
property</b>.</p>
</li>
<li><a name="line-buffering"></a><b>line buffering</b>
<p>Used by a <b>standard I/O</b> output stream that
flushes its <b>buffer</b> after every <b>newline</b>. Many standard I/O libraries
automatically set up line buffering on output that is going to the terminal.</p>
</li>
<li><a name="line-number"></a><b>line number</b>
<p>The number of lines read previous to this one, plus 1. Perl
keeps a separate line number for each source or input file it opens. The
current source file&#x2019;s line number is represented by <code class="inline"><span class="w">__LINE__</span></code>
. The
current input line number (for the file that was most recently read via
<code class="inline"><span class="q">&lt;FH&gt;</span></code>
) is represented by the <code class="inline"><span class="i">$.</span></code>
 (<code class="inline"><span class="i">$INPUT_LINE_NUMBER</span></code>
)
variable. Many error messages report both values, if available.</p>
</li>
<li><a name="link"></a><b>link</b>
<p>Used as a noun, a name in a <b>directory</b> that represents a
<b>file</b>. A given file can have multiple links to it. It&#x2019;s like having the
same phone number listed in the phone directory under different names. As a
verb, to resolve a partially <b>compiled</b> file&#x2019;s unresolved symbols into a
(nearly) executable image. Linking can generally be static or dynamic,
which has nothing to do with static or dynamic scoping.</p>
</li>
<li><a name="LIST"></a><b>LIST</b>
<p>A syntactic construct representing a
comma- separated list of expressions, evaluated to produce a <b>list value</b>.
Each <b>expression</b> in a <i><code class="inline"><span class="w">LIST</span></code>
</i> is evaluated in <b>list context</b> and
interpolated into the list value.</p>
</li>
<li><a name="list"></a><b>list</b>
<p>An ordered set of scalar values.</p>
</li>
<li><a name="list-context"></a><b>list context</b>
<p>The situation in which an <b>expression</b> is
expected by its surroundings (the code calling it) to return a list of
values rather than a single value. Functions that want a <i><code class="inline"><span class="w">LIST</span></code>
</i> of
arguments tell those arguments that they should produce a list value. See
also <b>context</b>.</p>
</li>
<li><a name="list-operator"></a><b>list operator</b>
<p>An <b>operator</b> that does something with a list of
values, such as <code class="inline"><a class="l_k" href="functions/join.html">join</a></code> or <code class="inline"><a class="l_k" href="functions/grep.html">grep</a></code>. Usually used for named built-in
operators (such as <code class="inline"><a class="l_k" href="functions/print.html">print</a></code>, <code class="inline"><a class="l_k" href="functions/unlink.html">unlink</a></code>, and <code class="inline"><a class="l_k" href="functions/system.html">system</a></code>) that do not require
parentheses around their <b>argument</b> list.</p>
</li>
<li><a name="list-value"></a><b>list value</b>
<p>An unnamed list of temporary scalar
values that may be passed around within a program from any list-generating
function to any function or construct that provides a <b>list context</b>.</p>
</li>
<li><a name="literal"></a><b>literal</b>
<p>A token in a programming language, such as a number or
<b>string</b>, that gives you an actual <b>value</b> instead of merely representing
possible values as a <b>variable</b> does.</p>
</li>
<li><a name="little-endian"></a><b>little-endian</b>
<p>From Swift: someone
who eats eggs little end first. Also used of computers that store the least
significant <b>byte</b> of a word at a lower byte address than the most
significant byte. Often considered superior to big-endian machines. See
also <b>big-endian</b>.</p>
</li>
<li><a name="local"></a><b>local</b>
<p>Not meaning the same thing everywhere. A global
variable in Perl can be localized inside a <b>dynamic scope</b> via the
<code class="inline"><a class="l_k" href="functions/local.html">local</a></code> operator.</p>
</li>
<li><a name="logical-operator"></a><b>logical operator</b>
<p>Symbols representing the concepts &#x201c;and&#x201d;, &#x201c;or&#x201d;,
&#x201c;xor&#x201d;, and &#x201c;not&#x201d;.</p>
</li>
<li><a name="lookahead"></a><b>lookahead</b>
<p>An <b>assertion</b> that peeks at the string to the right of the current match location.</p>
</li>
<li><a name="lookbehind"></a><b>lookbehind</b>
<p>An <b>assertion</b> that peeks at the string to the left of the current match
location.</p>
</li>
<li><a name="loop"></a><b>loop</b>
<p>A construct that
performs something repeatedly, like a roller coaster.</p>
</li>
<li><a name="loop-control-statement"></a><b>loop control statement</b>
<p>Any statement within the body of a loop that can
make a loop prematurely stop looping or skip an <b>iteration</b>. Generally,
you shouldn&#x2019;t try this on roller coasters.</p>
</li>
<li><a name="loop-label"></a><b>loop label</b>
<p>A kind of key or name attached to a loop (or
roller coaster) so that loop control statements can talk about which loop
they want to control.</p>
</li>
<li><a name="lowercase"></a><b>lowercase</b>
<p>In Unicode, not just
characters with the General Category of Lowercase Letter, but any character
with the Lowercase property, including Modifier Letters, Letter Numbers,
some Other Symbols, and one Combining Mark.</p>
</li>
<li><a name="lvaluable"></a><b>lvaluable</b>
<p>Able to serve as an <b>lvalue</b>.</p>
</li>
<li><a name="lvalue"></a><b>lvalue</b>
<p>Term used by language lawyers for a
storage location you can assign a new <b>value</b> to, such as a <b>variable</b> or
an element of an <b>array</b>. The &#x201c;l&#x201d; is short for &#x201c;left&#x201d;, as in the left side
of an assignment, a typical place for lvalues. An <b>lvaluable</b> function or
expression is one to which a value may be assigned, as in <code class="inline"><a class="l_k" href="functions/pos.html">pos</a><span class="s">(</span><span class="i">$x</span><span class="s">)</span> = <span class="n">10</span></code>
.</p>
</li>
<li><a name="lvalue-modifier"></a><b>lvalue modifier</b>
<p>An adjectival pseudofunction that
warps the meaning of an <b>lvalue</b> in some declarative fashion. Currently
there are three lvalue modifiers: <code class="inline"><a class="l_k" href="functions/my.html">my</a></code>, <code class="inline"><a class="l_k" href="functions/our.html">our</a></code>, and <code class="inline"><a class="l_k" href="functions/local.html">local</a></code>.</p>
</li>
</ul>
<a name="M"></a><h2>M</h2>
<ul>
<li><a name="magic"></a><b>magic</b>
<p>Technically speaking, any extra semantics attached to a
variable such as <code class="inline"><span class="i">$!</span></code>
, <code class="inline"><span class="i">$0</span></code>
, <code class="inline"><span class="i">%ENV</span></code>
, or <code class="inline"><span class="i">%SIG</span></code>
, or to any tied
variable.  Magical things happen when you diddle those variables.</p>
</li>
<li><a name="magical-increment"></a><b>magical increment</b>
<p>An <b>increment</b> operator that knows how to
bump up ASCII alphabetics as well as numbers.</p>
</li>
<li><a name="magical-variables"></a><b>magical variables</b>
<p>Special variables that have side
effects when you access them or assign to them. For example, in Perl,
changing elements of the <code class="inline"><span class="i">%ENV</span></code>
 array also changes the corresponding
environment variables that subprocesses will use. Reading the <code class="inline"><span class="i">$!</span></code>

variable gives you the current system error number or message.</p>
</li>
<li><a name="Makefile"></a><b>Makefile</b>
<p>A file that controls the compilation of a program. Perl programs
don&#x2019;t usually need a <b>Makefile</b> because the Perl compiler has plenty of
self-control.</p>
</li>
<li><a name="man"></a><b>man</b>
<p>The Unix program that displays online documentation
(manual pages) for you.</p>
</li>
<li><a name="manpage"></a><b>manpage</b>
<p>A &#x201c;page&#x201d; from the manuals, typically accessed via the
<i>man</i>(1) command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of
BUGS, and so on, and is typically longer than a page. There are manpages
documenting <b>commands</b>, <b>syscalls</b>, <b>library</b> <b>functions</b>, <b>devices</b>,
<b>protocols</b>, <b>files</b>, and such. In this book, we call any piece of
standard Perl documentation (like <a href="perlop.html">perlop</a> or <a href="perldelta.html">perldelta</a>) a manpage, no
matter what format it&#x2019;s installed in on your system.</p>
</li>
<li><a name="matching"></a><b>matching</b>
<p>See <b>pattern matching</b>.</p>
</li>
<li><a name="member-data"></a><b>member data</b>
<p>See <b>instance variable</b>.</p>
</li>
<li><a name="memory"></a><b>memory</b>
<p>This always means your main memory, not your disk.
Clouding the issue is the fact that your machine may implement
<b>virtual</b> memory; that is, it will pretend that it has more memory than
it really does, and it&#x2019;ll use disk space to hold inactive bits. This can
make it seem like you have a little more memory than you really do, but
it&#x2019;s not a substitute for real memory. The best thing that can be said
about virtual memory is that it lets your performance degrade gradually
rather than suddenly when you run out of real memory. But your program
can die when you run out of virtual memory, too&#x2014;if you haven&#x2019;t thrashed
your disk to death first.</p>
</li>
<li><a name="metacharacter"></a><b>metacharacter</b>
<p>A <b>character</b> that is <i>not</i> supposed to be treated normally. Which characters
are to be treated specially as metacharacters varies greatly from context to
context. Your <b>shell</b> will have certain metacharacters, double-quoted Perl
<b>strings</b> have other metacharacters,
and <b>regular expression</b> patterns have all the double-quote metacharacters plus
some extra ones of their own.</p>
</li>
<li><a name="metasymbol"></a><b>metasymbol</b>
<p>Something we&#x2019;d call a
<b>metacharacter</b> except that it&#x2019;s a sequence of more than one character.
Generally, the first character in the sequence must be a true metacharacter
to get the other characters in the metasymbol to misbehave along with it.</p>
</li>
<li><a name="method"></a><b>method</b>
<p>A kind of action that an <b>object</b> can take if you tell
it to. See Camel chapter 12, &#x201c;Objects&#x201d;.</p>
</li>
<li><a name="method-resolution-order"></a><b>method resolution order</b>
<p>The path Perl takes through <code class="inline"><span class="i">@INC</span></code>
. By default, this is a double depth first
search, once looking for defined methods and once for <code class="inline">AUTOLOAD</code>
. However,
Perl lets you configure this with <code class="inline"><span class="w">mro</span></code>
.</p>
</li>
<li><a name="minicpan"></a><b>minicpan</b>
<p>A CPAN mirror that includes just the latest versions for each
distribution, probably created with <code class="inline"><span class="w">CPAN::Mini</span></code>
. See
Camel chapter 19, &#x201c;CPAN&#x201d;.</p>
</li>
<li><a name="minimalism"></a><b>minimalism</b>
<p>The belief that &#x201c;small is beautiful&#x201d;. Paradoxically, if you
say something in a small language, it turns out big, and if you say it in a
big language, it turns out small. Go figure.</p>
</li>
<li><a name="mode"></a><b>mode</b>
<p>In the context of the <i>stat</i>(2) syscall, refers to the field
holding the <b>permission bits</b> and the type of the <b>file</b>.</p>
</li>
<li><a name="modifier"></a><b>modifier</b>
<p>See <b>statement modifier</b>, <b>regular expression</b>, and
<b>lvalue</b>, not necessarily in that order.</p>
</li>
<li><a name="module"></a><b>module</b>
<p>A <b>file</b> that defines a <b>package</b> of (almost) the same
name, which can either <b>export</b> symbols or function as an <b>object</b> class.
(A module&#x2019;s main <i>.pm</i> file may also load in other files in support of the
module.) See the <code class="inline"><a class="l_k" href="functions/use.html">use</a></code> built-in.</p>
</li>
<li><a name="modulus"></a><b>modulus</b>
<p>An integer divisor when
you&#x2019;re interested in the remainder instead of the quotient.</p>
</li>
<li><a name="mojibake"></a><b>mojibake</b>
<p>When you speak one language and the computer thinks you&#x2019;re
speaking another. You&#x2019;ll see odd translations when you send UTF&#x2011;8, for
instance, but the computer thinks you sent Latin-1, showing all sorts of
weird characters instead. The term is written &#x300c;&#x6587;&#x5b57;&#x5316;&#x3051;&#x300d;in Japanese and
means &#x201c;character rot&#x201d;, an apt description. Pronounced [<code class="inline"><span class="w">mod&#x291;ibake</span></code>
] in
standard <b>IPA</b> phonetics, or approximately &#x201c;moh-jee-bah-keh&#x201d;.</p>
</li>
<li><a name="monger"></a><b>monger</b>
<p>Short for one member of <b>Perl mongers</b>, a
purveyor of Perl.</p>
</li>
<li><a name="mortal"></a><b>mortal</b>
<p>A temporary value scheduled to die when the
current statement finishes.</p>
</li>
<li><a name="mro"></a><b>mro</b>
<p>See <b>method resolution order</b>.</p>
</li>
<li><a name="multidimensional-array"></a><b>multidimensional array</b>
<p>An array with multiple
subscripts for finding a single element. Perl implements these using
<b>references</b>&#x2014;see Camel chapter 9, &#x201c;Data Structures&#x201d;.</p>
</li>
<li><a name="multiple-inheritance"></a><b>multiple inheritance</b>
<p>The features you got from
your mother and father, mixed together unpredictably. (See also
<b>inheritance</b> and <b>single inheritance</b>.) In computer languages (including
Perl), it is the notion that a given class may have multiple direct
ancestors or <b>base classes</b>.</p>
</li>
</ul>
<a name="N"></a><h2>N</h2>
<ul>
<li><a name="named-pipe"></a><b>named pipe</b>
<p>A <b>pipe</b> with a name embedded in the
<b>filesystem</b> so that it can be accessed by two unrelated <b>processes</b>.</p>
</li>
<li><a name="namespace"></a><b>namespace</b>
<p>A domain of names. You needn&#x2019;t worry about whether the
names in one such domain have been used in another. See <b>package</b>.</p>
</li>
<li><a name="NaN"></a><b>NaN</b>
<p>Not a number. The value Perl uses
for certain invalid or inexpressible floating-point operations.</p>
</li>
<li><a name="network-address"></a><b>network address</b>
<p>The most important attribute of a socket, like your
telephone&#x2019;s telephone number. Typically an IP address. See also <b>port</b>.</p>
</li>
<li><a name="newline"></a><b>newline</b>
<p>A single character that
represents the end of a line, with the ASCII value of 012 octal under Unix
(but 015 on a Mac), and represented by <code class="inline">\<span class="w">n</span></code>
 in Perl strings. For Windows
machines writing text files, and for certain physical devices like
terminals, the single newline gets automatically translated by your C
library into a line feed and a carriage return, but normally, no
translation is done.</p>
</li>
<li><a name="NFS"></a><b>NFS</b>
<p>Network File System, which allows you to mount a remote filesystem as if it were local.</p>
</li>
<li><a name="normalization"></a><b>normalization</b>
<p>Converting a text string into an alternate but equivalent
<b>canonical</b> (or compatible) representation that can then be compared for
equivalence. Unicode recognizes four different normalization forms: NFD,
NFC, NFKD, and NFKC.</p>
</li>
<li><a name="null-character"></a><b>null character</b>
<p>A character with the numeric value of
zero. It&#x2019;s used by C to terminate strings, but Perl allows strings to
contain a null.</p>
</li>
<li><a name="null-list"></a><b>null list</b>
<p>A <b>list value</b> with zero elements, represented
in Perl by <code class="inline"><span class="s">(</span><span class="s">)</span></code>
.</p>
</li>
<li><a name="null-string"></a><b>null string</b>
<p>A <b>string</b> containing no characters, not to
be confused with a string containing a <b>null character</b>, which has a
positive length and is <b>true</b>.</p>
</li>
<li><a name="numeric-context"></a><b>numeric context</b>
<p>The situation in which an expression
is expected by its surroundings (the code calling it) to return a number.
See also <b>context</b> and <b>string context</b>.</p>
</li>
<li><a name="numification"></a><b>numification</b>
<p>(Sometimes spelled <i>nummification</i> and <i>nummify</i>.) Perl lingo
for implicit conversion into a number; the related verb is <i>numify</i>.
<i>Numification</i> is intended to rhyme with <i>mummification</i>, and <i>numify</i> with
<i>mummify</i>. It is unrelated to English <i>numen</i>, <i>numina</i>, <i>numinous</i>. We
originally forgot the extra <i>m</i> a long time ago, and some people got used to
our funny spelling, and so just as with <code class="inline"><span class="w">HTTP_REFERER</span></code>
&#x2019;s own missing letter,
our weird spelling has stuck around.</p>
</li>
<li><a name="NV"></a><b>NV</b>
<p>Short for Nevada, no part of
which will ever be confused with civilization. NV also means an internal
floating- point Numeric Value of the type a <b>scalar</b> can hold, not to be
confused with an <b>IV</b>.</p>
</li>
<li><a name="nybble"></a><b>nybble</b>
<p>Half a <b>byte</b>, equivalent to one <b>hexadecimal</b> digit, and worth
four <b>bits</b>.</p>
</li>
</ul>
<a name="O"></a><h2>O</h2>
<ul>
<li><a name="object"></a><b>object</b>
<p>An <b>instance</b> of a <b>class</b>. Something that &#x201c;knows&#x201d;
what user-defined type (class) it is, and what it can do because of what
class it is. Your program can request an object to do things, but the
object gets to decide whether it wants to do them or not. Some objects are
more accommodating than others.</p>
</li>
<li><a name="octal"></a><b>octal</b>
<p>A number in base 8. Only the digits 0 through 7 are allowed. Octal
constants in Perl start with 0, as in 013. See also the <code class="inline"><a class="l_k" href="functions/oct.html">oct</a></code> function.</p>
</li>
<li><a name="offset"></a><b>offset</b>
<p>How many things you have to skip
over when moving from the beginning of a string or array to a specific
position within it. Thus, the minimum offset is zero, not one, because you
don&#x2019;t skip anything to get to the first item.</p>
</li>
<li><a name="one-liner"></a><b>one-liner</b>
<p>An entire computer program crammed into one line of
text.</p>
</li>
<li><a name="open-source-software"></a><b>open source software</b>
<p>Programs for which the source code is freely
available and freely redistributable, with no commercial strings attached.
For a more detailed definition, see <a href="http://www.opensource.org/osd.html">http://www.opensource.org/osd.html</a>.</p>
</li>
<li><a name="operand"></a><b>operand</b>
<p>An <b>expression</b> that yields a <b>value</b> that an
<b>operator</b> operates on. See also <b>precedence</b>.</p>
</li>
<li><a name="operating-system"></a><b>operating system</b>
<p>A special program that runs on the bare
machine and hides the gory details of managing <b>processes</b> and <b>devices</b>.
Usually used in a looser sense to indicate a particular culture of
programming. The loose sense can be used at varying levels of specificity.
At one extreme, you might say that all versions of Unix and Unix-lookalikes
are the same operating system (upsetting many people, especially lawyers
and other advocates). At the other extreme, you could say this particular
version of this particular vendor&#x2019;s operating system is different from any
other version of this or any other vendor&#x2019;s operating system. Perl is much
more portable across operating systems than many other languages. See also
<b>architecture</b> and <b>platform</b>.</p>
</li>
<li><a name="operator"></a><b>operator</b>
<p>A gizmo that transforms some number of input values to
some number of output values, often built into a language with a special
syntax or symbol. A given operator may have specific expectations about
what <b>types</b> of data you give as its arguments (<b>operands</b>) and what type
of data you want back from it.</p>
</li>
<li><a name="operator-overloading"></a><b>operator overloading</b>
<p>A kind of
<b>overloading</b> that you can do on built-in <b>operators</b> to make them work
on <b>objects</b> as if the objects were ordinary scalar values, but with the
actual semantics supplied by the object class. This is set up with the
overload <b>pragma</b>&#x2014;see Camel chapter 13, &#x201c;Overloading&#x201d;.</p>
</li>
<li><a name="options"></a><b>options</b>
<p>See either <b>switches</b> or <b>regular expression modifiers</b>.</p>
</li>
<li><a name="ordinal"></a><b>ordinal</b>
<p>An abstract character&#x2019;s integer value. Same thing as
<b>codepoint</b>.</p>
</li>
<li><a name="overloading"></a><b>overloading</b>
<p>Giving additional meanings to a symbol or construct.
Actually, all languages do overloading to one extent or another, since
people are good at figuring out things from <b>context</b>.</p>
</li>
<li><a name="overriding"></a><b>overriding</b>
<p>Hiding or invalidating some other definition of the
same name. (Not to be confused with <b>overloading</b>, which adds definitions
that must be disambiguated some other way.) To confuse the issue further,
we use the word with two overloaded definitions: to describe how you can
define your own <b>subroutine</b> to hide a built-in <b>function</b> of the same
name (see the section &#x201c;Overriding Built-in Functions&#x201d; in Camel chapter 11,
&#x201c;Modules&#x201d;), and to describe how you can define a replacement <b>method</b> in a
<b>derived class</b> to hide a <b>base class</b>&#x2019;s method of the same name (see
Camel chapter 12, &#x201c;Objects&#x201d;).</p>
</li>
<li><a name="owner"></a><b>owner</b>
<p>The one user (apart from the
superuser) who has absolute control over a <b>file</b>. A file may also have a
<b>group</b> of users who may exercise joint ownership if the real owner
permits it. See <b>permission bits</b>.</p>
</li>
</ul>
<a name="P"></a><h2>P</h2>
<ul>
<li><a name="package"></a><b>package</b>
<p>A <b>namespace</b> for global <b>variables</b>, <b>subroutines</b>,
and the like, such that they can be kept separate from like-named
<b>symbols</b> in other namespaces. In a sense, only the package is global,
since the symbols in the package&#x2019;s symbol table are only accessible from
code <b>compiled</b> outside the package by naming the package. But in another
sense, all package symbols are also globals&#x2014;they&#x2019;re just well-organized
globals.</p>
</li>
<li><a name="pad"></a><b>pad</b>
<p>Short for <b>scratchpad</b>.</p>
</li>
<li><a name="parameter"></a><b>parameter</b>
<p>See <b>argument</b>.</p>
</li>
<li><a name="parent-class"></a><b>parent class</b>
<p>See <b>base class</b>.</p>
</li>
<li><a name="parse-tree"></a><b>parse tree</b>
<p>See <b>syntax tree</b>.</p>
</li>
<li><a name="parsing"></a><b>parsing</b>
<p>The subtle but sometimes brutal art of attempting to turn
your possibly malformed program into a valid <b>syntax tree</b>.</p>
</li>
<li><a name="patch"></a><b>patch</b>
<p>To fix by applying one, as it were. In the realm of hackerdom, a
listing of the differences between two versions of a program as might be
applied by the <b>patch</b>(1) program when you want to fix a bug or upgrade
your old version.</p>
</li>
<li><a name="PATH"></a><b>PATH</b>
<p>The list of
<b>directories</b> the system searches to find a program you want to
<b>execute</b>.  The list is stored as one of your <b>environment variables</b>,
accessible in Perl as <code class="inline"><span class="i">$ENV</span>{<span class="w">PATH</span>}</code>
.</p>
</li>
<li><a name="pathname"></a><b>pathname</b>
<p>A fully qualified filename such as <i>/usr/bin/perl</i>. Sometimes
confused with <code class="inline"><span class="w">PATH</span></code>
.</p>
</li>
<li><a name="pattern"></a><b>pattern</b>
<p>A template used in <b>pattern matching</b>.</p>
</li>
<li><a name="pattern-matching"></a><b>pattern matching</b>
<p>Taking a pattern, usually a <b>regular
expression</b>, and trying the pattern various ways on a string to see whether
there&#x2019;s any way to make it fit. Often used to pick interesting tidbits out
of a file.</p>
</li>
<li><a name="PAUSE"></a><b>PAUSE</b>
<p>The Perl Authors Upload SErver (<a href="http://pause.perl.org">http://pause.perl.org</a>), the gateway
for <b>modules</b> on their way to <b>CPAN</b>.</p>
</li>
<li><a name="Perl-mongers"></a><b>Perl mongers</b>
<p>A Perl user group, taking the form of its
name from the New York Perl mongers, the first Perl user group. Find one
near you at <a href="http://www.pm.org">http://www.pm.org</a>.</p>
</li>
<li><a name="permission-bits"></a><b>permission bits</b>
<p>Bits that the <b>owner</b> of a file sets
or unsets to allow or disallow access to other people. These flag bits are
part of the <b>mode</b> word returned by the <code class="inline"><a class="l_k" href="functions/stat.html">stat</a></code> built-in when you ask
about a file. On Unix systems, you can check the <i>ls</i>(1) manpage for more
information.</p>
</li>
<li><a name="Pern"></a><b>Pern</b>
<p>What you get when you do <code class="inline"><span class="w">Perl</span>++</code>
 twice. Doing it only once
will curl your hair. You have to increment it eight times to shampoo your
hair. Lather, rinse, iterate.</p>
</li>
<li><a name="pipe"></a><b>pipe</b>
<p>A direct <b>connection</b> that carries the output of one
<b>process</b> to the input of another without an intermediate temporary file.
Once the pipe is set up, the two processes in question can read and write
as if they were talking to a normal file, with some caveats.</p>
</li>
<li><a name="pipeline"></a><b>pipeline</b>
<p>A series of <b>processes</b> all in a row, linked by <b>pipes</b>, where
each passes its output stream to the next.</p>
</li>
<li><a name="platform"></a><b>platform</b>
<p>The entire hardware and software context in which a
program runs. A program written in a platform-dependent language might
break if you change any of the following: machine, operating system,
libraries, compiler, or system configuration. The <i>perl</i> interpreter has
to be <b>compiled</b> differently for each platform because it is implemented
in C, but programs written in the Perl language are largely platform
independent.</p>
</li>
<li><a name="pod"></a><b>pod</b>
<p>The markup
used to embed documentation into your Perl code. Pod stands for &#x201c;Plain old
documentation&#x201d;. See Camel chapter 23, &#x201c;Plain Old Documentation&#x201d;.</p>
</li>
<li><a name="pod-command"></a><b>pod command</b>
<p>A sequence, such as <code class="inline"><span class="pd">=head1</span></code>
, that denotes
the start of a <b>pod</b> section.</p>
</li>
<li><a name="pointer"></a><b>pointer</b>
<p>A <b>variable</b> in a language like C that contains the exact
memory location of some other item. Perl handles pointers internally so you
don&#x2019;t have to worry about them. Instead, you just use symbolic pointers in
the form of <b>keys</b> and <b>variable</b> names, or <b>hard references</b>, which
aren&#x2019;t pointers (but act like pointers and do in fact contain pointers).</p>
</li>
<li><a name="polymorphism"></a><b>polymorphism</b>
<p>The notion that you can tell an <b>object</b> to do something
generic, and the object will interpret the command in different ways
depending on its type. [&lt; Greek &#x3c0;&#x3bf;&#x3bb;&#x3c5;- + &#x3bc;&#x3bf;&#x3c1;&#x3d5;&#x3ae;, many forms.]</p>
</li>
<li><a name="port"></a><b>port</b>
<p>The part of the address of a TCP or UDP socket that directs
packets to the correct process after finding the right machine, something
like the phone extension you give when you reach the company operator. Also
the result of converting code to run on a different platform than
originally intended, or the verb denoting this conversion.</p>
</li>
<li><a name="portable"></a><b>portable</b>
<p>Once upon a time, C code compilable under both BSD and
SysV. In general, code that can be easily converted to run on another
<b>platform</b>, where &#x201c;easily&#x201d; can be defined however you like, and usually
is.  Anything may be considered portable if you try hard enough, such as a
mobile home or London Bridge.</p>
</li>
<li><a name="porter"></a><b>porter</b>
<p>Someone who &#x201c;carries&#x201d; software from one <b>platform</b> to another.
Porting programs written in platform-dependent languages such as C can be
difficult work, but porting programs like Perl is very much worth the
agony.</p>
</li>
<li><a name="possessive"></a><b>possessive</b>
<p>Said of quantifiers and groups in patterns that refuse
to give up anything once they&#x2019;ve gotten their mitts on it. Catchier and
easier to say than the even more formal <i>nonbacktrackable</i>.</p>
</li>
<li><a name="POSIX"></a><b>POSIX</b>
<p>The Portable Operating System Interface
specification.</p>
</li>
<li><a name="postfix"></a><b>postfix</b>
<p>An <b>operator</b> that follows its <b>operand</b>, as in
<code class="inline"><span class="i">$x</span>++</code>
.</p>
</li>
<li><a name="pp"></a><b>pp</b>
<p>An internal shorthand for a
&#x201c;push- pop&#x201d; code; that is, C code implementing Perl&#x2019;s stack machine.</p>
</li>
<li><a name="pragma"></a><b>pragma</b>
<p>A standard module whose practical hints and
suggestions are received (and possibly ignored) at compile time. Pragmas
are named in all lowercase.</p>
</li>
<li><a name="precedence"></a><b>precedence</b>
<p>The rules of
conduct that, in the absence of other guidance, determine what should
happen first.  For example, in the absence of parentheses, you always do
multiplication before addition.</p>
</li>
<li><a name="prefix"></a><b>prefix</b>
<p>An <b>operator</b> that precedes its <b>operand</b>, as in
<code class="inline">++<span class="i">$x</span></code>
.</p>
</li>
<li><a name="preprocessing"></a><b>preprocessing</b>
<p>What some helper <b>process</b> did to transform the incoming
data into a form more suitable for the current process. Often done with an
incoming <b>pipe</b>. See also <b>C preprocessor</b>.</p>
</li>
<li><a name="primary-maintainer"></a><b>primary maintainer</b>
<p>The author that PAUSE allows to assign <b>co-maintainer</b>
permissions to a <b>namespace</b>. A primary maintainer can give up this
distinction by assigning it to another PAUSE author. See Camel chapter 19,
&#x201c;CPAN&#x201d;.</p>
</li>
<li><a name="procedure"></a><b>procedure</b>
<p>A <b>subroutine</b>.</p>
</li>
<li><a name="process"></a><b>process</b>
<p>An instance of a running program. Under multitasking
systems like Unix, two or more separate processes could be running the same
program independently at the same time&#x2014;in fact, the <code class="inline"><a class="l_k" href="functions/fork.html">fork</a></code> function is
designed to bring about this happy state of affairs. Under other operating
systems, processes are sometimes called &#x201c;threads&#x201d;, &#x201c;tasks&#x201d;, or &#x201c;jobs&#x201d;,
often with slight nuances in meaning.</p>
</li>
<li><a name="program"></a><b>program</b>
<p>See <b>script</b>.</p>
</li>
<li><a name="program-generator"></a><b>program generator</b>
<p>A system that algorithmically writes code for you in a
high-level language. See also <b>code generator</b>.</p>
</li>
<li><a name="progressive-matching"></a><b>progressive matching</b>
<p><b>Pattern matching</b>  matching&gt;that picks up where it left off before.</p>
</li>
<li><a name="property"></a><b>property</b>
<p>See either <b>instance variable</b> or <b>character property</b>.</p>
</li>
<li><a name="protocol"></a><b>protocol</b>
<p>In networking, an agreed-upon way of sending messages
back and forth so that neither correspondent will get too confused.</p>
</li>
<li><a name="prototype"></a><b>prototype</b>
<p>An optional part of a <b>subroutine</b> declaration telling
the Perl compiler how many and what flavor of arguments may be passed as
<b>actual arguments</b>, so you can write subroutine calls that parse much like
built-in functions. (Or don&#x2019;t parse, as the case may be.)</p>
</li>
<li><a name="pseudofunction"></a><b>pseudofunction</b>
<p>A construct that sometimes looks like a function but really
isn&#x2019;t. Usually reserved for <b>lvalue</b> modifiers like <code class="inline"><a class="l_k" href="functions/my.html">my</a></code>, for <b>context</b>
modifiers like <code class="inline"><a class="l_k" href="functions/scalar.html">scalar</a></code>, and for the pick-your-own-quotes constructs,
<code class="inline"><a class="l_k" href="functions/q.html">q//</a></code>, <code class="inline"><a class="l_k" href="functions/qq.html">qq//</a></code>, <code class="inline"><a class="l_k" href="functions/qx.html">qx//</a></code>, <code class="inline"><a class="l_k" href="functions/qw.html">qw//</a></code>, <code class="inline"><a class="l_k" href="functions/qr.html">qr//</a></code>, <code class="inline"><a class="l_k" href="functions/m.html">m//</a></code>, <code class="inline"><a class="l_k" href="functions/s.html">s///</a></code>, <code class="inline"><a class="l_k" href="functions/y.html">y///</a></code>, and
<code class="inline"><a class="l_k" href="functions/tr.html">tr///</a></code>.</p>
</li>
<li><a name="pseudohash"></a><b>pseudohash</b>
<p>Formerly, a reference to an array
whose initial element happens to hold a reference to a hash. You used to be
able to treat a pseudohash reference as either an array reference or a hash
reference. Pseduohashes are no longer supported.</p>
</li>
<li><a name="pseudoliteral"></a><b>pseudoliteral</b>
<p>An <b>operator</b> X<code class="inline">that looks something like a <b>literal</b>,
such as the output-grabbing operator, &lt;literal
moreinfo="none"</code>`&gt;<i><code class="inline"><span class="w">command</span></code>
</i><code class="inline">`</code>.</p>
</li>
<li><a name="public-domain"></a><b>public domain</b>
<p>Something not owned by anybody. Perl is copyrighted and is
thus <i>not</i> in the public domain&#x2014;it&#x2019;s just <b>freely available</b> and <b>freely
redistributable</b>.</p>
</li>
<li><a name="pumpkin"></a><b>pumpkin</b>
<p>A notional &#x201c;baton&#x201d; handed around the Perl community
indicating who is the lead integrator in some arena of development.</p>
</li>
<li><a name="pumpking"></a><b>pumpking</b>
<p>A <b>pumpkin</b> holder, the person in charge of pumping the pump,
or at least priming it. Must be willing to play the part of the Great
Pumpkin now and then.</p>
</li>
<li><a name="PV"></a><b>PV</b>
<p>A &#x201c;pointer value&#x201d;, which is Perl
Internals Talk for a <code class="inline"><span class="w">char</span>*</code>
.</p>
</li>
</ul>
<a name="Q"></a><h2>Q</h2>
<ul>
<li><a name="qualified"></a><b>qualified</b>
<p>Possessing a complete name. The symbol <code class="inline"><span class="i">$Ent::moot</span></code>
 is
qualified; <code class="inline"><span class="i">$moot</span></code>
 is unqualified. A fully qualified filename is specified
from the top-level directory.</p>
</li>
<li><a name="quantifier"></a><b>quantifier</b>
<p>A component of a <b>regular expression</b> specifying how
many times the foregoing <b>atom</b> may occur.</p>
</li>
</ul>
<a name="R"></a><h2>R</h2>
<ul>
<li><a name="race-condition"></a><b>race condition</b>
<p>A race condition exists when the result of
several interrelated events depends on the ordering of those events, but
that order cannot be guaranteed due to nondeterministic timing effects. If
two or more programs, or parts of the same program, try to go through the
same series of events, one might interrupt the work of the other. This is a
good way to find an <b>exploit</b>.</p>
</li>
<li><a name="readable"></a><b>readable</b>
<p>With respect to files, one that has the proper permission
bit set to let you access the file. With respect to computer programs, one
that&#x2019;s written well enough that someone has a chance of figuring out what
it&#x2019;s trying to do.</p>
</li>
<li><a name="reaping"></a><b>reaping</b>
<p>The last rites performed by a parent <b>process</b>
on behalf of a deceased child process so that it doesn&#x2019;t remain a
<b>zombie</b>.  See the <code class="inline"><a class="l_k" href="functions/wait.html">wait</a></code> and <code class="inline"><a class="l_k" href="functions/waitpid.html">waitpid</a></code> function calls.</p>
</li>
<li><a name="record"></a><b>record</b>
<p>A set of related data values in a <b>file</b> or <b>stream</b>,
often associated with a unique <b>key</b> field. In Unix, often commensurate
with a <b>line</b>, or a blank-line&#x2013;terminated set of lines (a &#x201c;paragraph&#x201d;).
Each line of the <i>/etc/passwd</i> file is a record, keyed on login name,
containing information about that user.</p>
</li>
<li><a name="recursion"></a><b>recursion</b>
<p>The art of defining something (at least partly) in
terms of itself, which is a naughty no-no in dictionaries but often works
out okay in computer programs if you&#x2019;re careful not to recurse forever
(which is like an infinite loop with more spectacular failure modes).</p>
</li>
<li><a name="reference"></a><b>reference</b>
<p>Where you look to find a pointer to information
somewhere else. (See <b>indirection</b>.) References come in two flavors:
<b>symbolic references</b> and <b>hard references</b>.</p>
</li>
<li><a name="referent"></a><b>referent</b>
<p>Whatever a reference refers to, which may or may not
have a name. Common types of referents include scalars, arrays, hashes, and
subroutines.</p>
</li>
<li><a name="regex"></a><b>regex</b>
<p>See <b>regular expression</b>.</p>
</li>
<li><a name="regular-expression"></a><b>regular expression</b>
<p>A single entity with various
interpretations, like an elephant. To a computer scientist, it&#x2019;s a grammar
for a little language in which some strings are legal and others aren&#x2019;t. To
normal people, it&#x2019;s a pattern you can use to find what you&#x2019;re looking for
when it varies from case to case. Perl&#x2019;s regular expressions are far from
regular in the theoretical sense, but in regular use they work quite well.
Here&#x2019;s a regular expression: <code class="inline"><span class="q">/Oh s.*t./</span></code>
. This will match strings like
&#x201c;<code class="inline"><span class="w">Oh</span> <a class="l_k" href="functions/say.html">say</a> <span class="i">can</span> <span class="w">you</span> <span class="w">see</span> <span class="w">by</span> <span class="w">the</span> <span class="w">dawn&#39;s</span> <span class="w">early</span> <span class="w">light</span></code>
&#x201d; and &#x201c;<code class="inline"><span class="w">Oh</span> <span class="w">sit</span>!</code>
&#x201d;. See
Camel chapter 5, &#x201c;Pattern Matching&#x201d;.</p>
</li>
<li><a name="regular-expression-modifier"></a><b>regular expression modifier</b>
<p>An option on a pattern or substitution, such as <code class="inline">/i</code> to render the pattern
case- insensitive.</p>
</li>
<li><a name="regular-file"></a><b>regular file</b>
<p>A <b>file</b> that&#x2019;s not a <b>directory</b>, a
<b>device</b>, a named <b>pipe</b> or <b>socket</b>, or a <b>symbolic link</b>. Perl uses
the <code class="inline"><span class="q">&ndash;f</span></code>
 file test operator to identify regular files. Sometimes called a
&#x201c;plain&#x201d; file.</p>
</li>
<li><a name="relational-operator"></a><b>relational operator</b>
<p>An <b>operator</b> that says whether a particular
ordering relationship is <b>true</b> about a pair of <b>operands</b>. Perl has both
numeric and string relational operators. See <b>collating sequence</b>.</p>
</li>
<li><a name="reserved-words"></a><b>reserved words</b>
<p>A word with a specific, built-in meaning
to a <b>compiler</b>, such as <code class="inline">if</code>
 or <code class="inline"><a class="l_k" href="functions/delete.html">delete</a></code>. In many languages (not Perl),
it&#x2019;s illegal to use reserved words to name anything else. (Which is why
they&#x2019;re reserved, after all.) In Perl, you just can&#x2019;t use them to name
<b>labels</b> or <b>filehandles</b>. Also called &#x201c;keywords&#x201d;.</p>
</li>
<li><a name="return-value"></a><b>return value</b>
<p>The <b>value</b> produced by a <b>subroutine</b>
or <b>expression</b> when evaluated. In Perl, a return value may be either a
<b>list</b> or a <b>scalar</b>.</p>
</li>
<li><a name="RFC"></a><b>RFC</b>
<p>Request For Comment, which despite the timid connotations is the name of a series of
important standards documents.</p>
</li>
<li><a name="right-shift"></a><b>right shift</b>
<p>A <b>bit shift</b> that divides
a number by some power of 2.</p>
</li>
<li><a name="role"></a><b>role</b>
<p>A name for a concrete set of behaviors. A role is a way to
add behavior to a class without inheritance.</p>
</li>
<li><a name="root"></a><b>root</b>
<p>The superuser (<code class="inline"><span class="w">UID</span></code>
 == 0). Also the top-level directory of
the filesystem.</p>
</li>
<li><a name="RTFM"></a><b>RTFM</b>
<p>What you are told when someone thinks you should Read The
Fine Manual.</p>
</li>
<li><a name="run-phase"></a><b>run phase</b>
<p>Any time after Perl starts running your main program.
See also <b>compile phase</b>. Run phase is mostly spent in <b>runtime</b> but may
also be spent in <b>compile time</b> when <code class="inline"><a class="l_k" href="functions/require.html">require</a></code>, <code class="inline"><a class="l_k" href="functions/do.html">do</a></code> <i><code class="inline"><span class="w">FILE</span></code>
</i>, or
<code class="inline"><a class="l_k" href="functions/eval.html">eval</a></code> <i><code class="inline"><span class="w">STRING</span></code>
</i> operators are executed, or when a substitution uses
the <code class="inline">/ee</code> modifier.</p>
</li>
<li><a name="runtime"></a><b>runtime</b>
<p>The time when Perl is actually doing what your
code says to do, as opposed to the earlier period of time when it was
trying to figure out whether what you said made any sense whatsoever, which
is <b>compile time</b>.</p>
</li>
<li><a name="runtime-pattern"></a><b>runtime pattern</b>
<p>A pattern that contains one or more
variables to be interpolated before parsing the pattern as a <b>regular
expression</b>, and that therefore cannot be analyzed at compile time, but
must be reanalyzed each time the pattern match operator is evaluated.
Runtime patterns are useful but expensive.</p>
</li>
<li><a name="RV"></a><b>RV</b>
<p>A recreational vehicle, not
to be confused with vehicular recreation. RV also means an internal
Reference Value of the type a <b>scalar</b> can hold. See also <b>IV</b> and <b>NV</b>
if you&#x2019;re not confused yet.</p>
</li>
<li><a name="rvalue"></a><b>rvalue</b>
<p>A <b>value</b> that you might find on the
right side of an <b>assignment</b>. See also <b>lvalue</b>.</p>
</li>
</ul>
<a name="S"></a><h2>S</h2>
<ul>
<li><a name="sandbox"></a><b>sandbox</b>
<p>A walled off area that&#x2019;s not supposed to affect beyond
its walls. You let kids play in the sandbox instead of running in the road.
See Camel chapter 20, &#x201c;Security&#x201d;.</p>
</li>
<li><a name="scalar"></a><b>scalar</b>
<p>A simple, singular value; a number, <b>string</b>, or
<b>reference</b>.</p>
</li>
<li><a name="scalar-context"></a><b>scalar context</b>
<p>The situation in which an
<b>expression</b> is expected by its surroundings (the code calling it) to
return a single <b>value</b> rather than a <b>list</b> of values. See also
<b>context</b> and <b>list context</b>. A scalar context sometimes imposes
additional constraints on the return value&#x2014;see <b>string context</b> and
<b>numeric context</b>. Sometimes we talk about a <b>Boolean context</b> inside
conditionals, but this imposes no additional constraints, since any scalar
value, whether numeric or <b>string</b>, is already true or false.</p>
</li>
<li><a name="scalar-literal"></a><b>scalar literal</b>
<p>A number or quoted <b>string</b>&#x2014;an actual
<b>value</b> in the text of your program, as opposed to a <b>variable</b>.</p>
</li>
<li><a name="scalar-value"></a><b>scalar value</b>
<p>A value that happens to be a
<b>scalar</b> as opposed to a <b>list</b>.</p>
</li>
<li><a name="scalar-variable"></a><b>scalar variable</b>
<p>A <b>variable</b> prefixed with
<code class="inline"><span class="i">$</span></code>
 that holds a single value.</p>
</li>
<li><a name="scope"></a><b>scope</b>
<p>From how far away you can see a variable, looking through
one. Perl has two visibility mechanisms. It does <b>dynamic scoping</b> of
<code class="inline"><a class="l_k" href="functions/local.html">local</a></code> <b>variables</b>, meaning that the rest of the <b>block</b>, and any
<b>subroutines</b> that are called by the rest of the block, can see the
variables that are local to the block. Perl does <b>lexical scoping</b> of
<code class="inline"><a class="l_k" href="functions/my.html">my</a></code> variables, meaning that the rest of the block can see the variable,
but other subroutines called by the block <i>cannot</i> see the variable.</p>
</li>
<li><a name="scratchpad"></a><b>scratchpad</b>
<p>The area in which a particular invocation of a particular
file or subroutine keeps some of its temporary values, including any
lexically scoped variables.</p>
</li>
<li><a name="script"></a><b>script</b>
<p>A text <b>file</b> that is a program
intended to be <b>executed</b> directly rather than <b>compiled</b> to another form
of file before <b>execution</b>.</p>
<p>Also, in the context of <b>Unicode</b>, a writing system for a particular
language or group of languages, such as Greek, Bengali, or Tengwar.</p>
</li>
<li><a name="script-kiddie"></a><b>script kiddie</b>
<p>A <b>cracker</b> who is not a <b>hacker</b> but knows just enough
to run canned scripts. A <b>cargo-cult</b> programmer.</p>
</li>
<li><a name="sed"></a><b>sed</b>
<p>A venerable Stream EDitor from
which Perl derives some of its ideas.</p>
</li>
<li><a name="semaphore"></a><b>semaphore</b>
<p>A fancy kind of interlock that prevents multiple <b>threads</b> or
<b>processes</b> from using up the same resources simultaneously.</p>
</li>
<li><a name="separator"></a><b>separator</b>
<p>A <b>character</b> or <b>string</b> that keeps two surrounding strings from being
confused with each other. The <code class="inline"><a class="l_k" href="functions/split.html">split</a></code> function works on separators. Not to be confused with <b>delimiters</b>
or <b>terminators</b>. The &#x201c;or&#x201d; in the previous sentence separated the two
alternatives.</p>
</li>
<li><a name="serialization"></a><b>serialization</b>
<p>Putting a fancy <b>data structure</b> into
linear order so that it can be stored as a <b>string</b> in a disk file or
database, or sent through a <b>pipe</b>. Also called marshalling.</p>
</li>
<li><a name="server"></a><b>server</b>
<p>In networking, a <b>process</b> that
either advertises a <b>service</b> or just hangs around at a known location and
waits for <b>clients</b> who need service to get in touch with it.</p>
</li>
<li><a name="service"></a><b>service</b>
<p>Something you do for someone else to make them happy,
like giving them the time of day (or of their life). On some machines,
well-known services are listed by the <code class="inline"><a class="l_k" href="functions/getservent.html">getservent</a></code>
function.</p>
</li>
<li><a name="setgid"></a><b>setgid</b>
<p>Same as <b>setuid</b>, only having to do with giving
away <b>group</b> privileges.</p>
</li>
<li><a name="setuid"></a><b>setuid</b>
<p>Said of a program that runs with the privileges of
its <b>owner</b> rather than (as is usually the case) the privileges of whoever
is running it. Also describes the bit in the mode word (<b>permission bits</b>)
that controls the feature. This bit must be explicitly set by the owner to
enable this feature, and the program must be carefully written not to give
away more privileges than it ought to.</p>
</li>
<li><a name="shared-memory"></a><b>shared memory</b>
<p>A piece of <b>memory</b> accessible by two
different <b>processes</b> who otherwise would not see each other&#x2019;s memory.</p>
</li>
<li><a name="shebang"></a><b>shebang</b>
<p>Irish for the whole McGillicuddy. In Perl culture, a
portmanteau of &#x201c;sharp&#x201d; and &#x201c;bang&#x201d;, meaning the <code class="inline"><span class="c">#!</span></code>
 sequence that tells
the system where to find the interpreter.</p>
</li>
<li><a name="shell"></a><b>shell</b>
<p>A <b>command</b>-line <b>interpreter</b>. The program that
interactively gives you a prompt, accepts one or more <b>lines</b> of input,
and executes the programs you mentioned, feeding each of them their proper
<b>arguments</b> and input data. Shells can also execute scripts containing
such commands. Under Unix, typical shells include the Bourne shell
(<i>/bin/sh</i>), the C shell (<i>/bin/csh</i>), and the Korn shell (<i>/bin/ksh</i>).
Perl is not strictly a shell because it&#x2019;s not interactive (although Perl
programs can be interactive).</p>
</li>
<li><a name="side-effects"></a><b>side effects</b>
<p>Something extra that happens when you evaluate an
<b>expression</b>. Nowadays it can refer to almost anything. For example,
evaluating a simple assignment statement typically has the &#x201c;side effect&#x201d; of
assigning a value to a variable. (And you thought assigning the value was
your primary intent in the first place!) Likewise, assigning a value to the
special variable <code class="inline"><span class="i">$|</span></code>
 (<code class="inline"><span class="i">$AUTOFLUSH</span></code>
) has the side effect of forcing a
flush after every <code class="inline"><a class="l_k" href="functions/write.html">write</a></code> or <code class="inline"><a class="l_k" href="functions/print.html">print</a></code> on the currently selected
filehandle.</p>
</li>
<li><a name="sigil"></a><b>sigil</b>
<p>A glyph used in magic. Or, for Perl, the symbol in front
of a variable name, such as <code class="inline"><span class="i">$</span></code>
, <code class="inline"><span class="i">@</span></code>
, and <code class="inline"><span class="i">%</span></code>
.</p>
</li>
<li><a name="signal"></a><b>signal</b>
<p>A bolt out of the blue; that is, an
event triggered by the <b>operating system</b>, probably when you&#x2019;re least
expecting it.</p>
</li>
<li><a name="signal-handler"></a><b>signal handler</b>
<p>A <b>subroutine</b> that, instead of being content to be
called in the normal fashion, sits around waiting for a bolt out of the
blue before it will deign to <b>execute</b>. Under Perl, bolts out of the blue
are called signals, and you send them with the <code class="inline"><a class="l_k" href="functions/kill.html">kill</a></code> built-in. See the
<code class="inline"><span class="i">%SIG</span></code>
 hash in Camel chapter 25, &#x201c;Special Names&#x201d; and the section &#x201c;Signals&#x201d;
in Camel chapter 15, &#x201c;Interprocess Communication&#x201d;.</p>
</li>
<li><a name="single-inheritance"></a><b>single inheritance</b>
<p>The features you got from your
mother, if she told you that you don&#x2019;t have a father. (See also
<b>inheritance</b> and <b>multiple inheritance</b>.) In computer languages, the
idea that <b>classes</b> reproduce asexually so that a given class can only
have one direct ancestor or <b>base class</b>. Perl supplies no such
restriction, though you may certainly program Perl that way if you like.</p>
</li>
<li><a name="slice"></a><b>slice</b>
<p>A selection of any number of
<b>elements</b> from a <b>list</b>, <b>array</b>, or <b>hash</b>.</p>
</li>
<li><a name="slurp"></a><b>slurp</b>
<p>To read an entire <b>file</b> into a <b>string</b> in one operation.</p>
</li>
<li><a name="socket"></a><b>socket</b>
<p>An endpoint for network communication among multiple
<b>processes</b> that works much like a telephone or a post office box. The
most important thing about a socket is its <b>network address</b> (like a phone
number). Different kinds of sockets have different kinds of addresses&#x2014;some
look like filenames, and some don&#x2019;t.</p>
</li>
<li><a name="soft-reference"></a><b>soft reference</b>
<p>See <b>symbolic reference</b>.</p>
</li>
<li><a name="source-filter"></a><b>source filter</b>
<p>A special kind of <b>module</b> that does
<b>preprocessing</b> on your script just before it gets to the <b>tokener</b>.</p>
</li>
<li><a name="stack"></a><b>stack</b>
<p>A device you can put things on the top of, and later take
them back off in the opposite order in which you put them on. See <b>LIFO</b>.</p>
</li>
<li><a name="standard"></a><b>standard</b>
<p>Included in the official Perl distribution, as in a
standard module, a standard tool, or a standard Perl <b>manpage</b>.</p>
</li>
<li><a name="standard-error"></a><b>standard error</b>
<p>The default output <b>stream</b> for nasty remarks that don&#x2019;t belong in
<b>standard output</b>. Represented within a Perl program by the output&gt;  <b>filehandle</b> <code class="inline"><span class="w">STDERR</span></code>
. You can use this
stream explicitly, but the <code class="inline"><a class="l_k" href="functions/die.html">die</a></code> and <code class="inline"><a class="l_k" href="functions/warn.html">warn</a></code> built-ins write to your
standard error stream automatically (unless trapped or otherwise
intercepted).</p>
</li>
<li><a name="standard-input"></a><b>standard input</b>
<p>The default input <b>stream</b> for your program,
which if possible shouldn&#x2019;t care where its data is coming from. Represented
within a Perl program by the <b>filehandle</b> <code class="inline"><span class="w">STDIN</span></code>
.</p>
</li>
<li><a name="standard-I%2fO"></a><b>standard I/O</b>
<p>A standard C library for doing <b>buffered</b> input
and output to the <b>operating system</b>. (The &#x201c;standard&#x201d; of standard I/O is
at most marginally related to the &#x201c;standard&#x201d; of standard input and output.)
In general, Perl relies on whatever implementation of standard I/O a given
operating system supplies, so the buffering characteristics of a Perl
program on one machine may not exactly match those on another machine.
Normally this only influences efficiency, not semantics. If your standard
I/O package is doing block buffering and you want it to <b>flush</b> the buffer
more often, just set the <code class="inline"><span class="i">$|</span></code>
 variable to a true value.</p>
</li>
<li><a name="Standard-Library"></a><b>Standard Library</b>
<p>Everything that comes with the official
<i>perl</i> distribution. Some vendor versions of <i>perl</i> change their
distributions, leaving out some parts or including extras. See also
<b>dual-lived</b>.</p>
</li>
<li><a name="standard-output"></a><b>standard output</b>
<p>The default output <b>stream</b> for your program,
which if possible shouldn&#x2019;t care where its data is going. Represented
within a Perl program by the <b>filehandle</b> <code class="inline"><span class="w">STDOUT</span></code>
.</p>
</li>
<li><a name="statement"></a><b>statement</b>
<p>A <b>command</b> to the computer about what to do next,
like a step in a recipe: &#x201c;Add marmalade to batter and mix until mixed.&#x201d; A
statement is distinguished from a <b>declaration</b>, which doesn&#x2019;t tell the
computer to do anything, but just to learn something.</p>
</li>
<li><a name="statement-modifier"></a><b>statement modifier</b>
<p>A <b>conditional</b> or
<b>loop</b> that you put after the <b>statement</b> instead of before, if you know
what we mean.</p>
</li>
<li><a name="static"></a><b>static</b>
<p>Varying slowly compared to something else. (Unfortunately,
everything is relatively stable compared to something else, except for
certain elementary particles, and we&#x2019;re not so sure about them.) In
computers, where things are supposed to vary rapidly, &#x201c;static&#x201d; has a
derogatory connotation, indicating a slightly dysfunctional <b>variable</b>,
<b>subroutine</b>, or <b>method</b>. In Perl culture, the word is politely avoided.</p>
<p>If you&#x2019;re a C or C++ programmer, you might be looking for Perl&#x2019;s <code class="inline"><a class="l_k" href="functions/state.html">state</a></code>
keyword.</p>
</li>
<li><a name="static-method"></a><b>static method</b>
<p>No such thing. See <b>class method</b>.</p>
</li>
<li><a name="static-scoping"></a><b>static scoping</b>
<p>No such thing. See <b>lexical scoping</b>.</p>
</li>
<li><a name="static-variable"></a><b>static variable</b>
<p>No such thing. Just use a <b>lexical
variable</b> in a scope larger than your <b>subroutine</b>, or declare it with
<code class="inline"><a class="l_k" href="functions/state.html">state</a></code> instead of with <code class="inline"><a class="l_k" href="functions/my.html">my</a></code>.</p>
</li>
<li><a name="stat-structure"></a><b>stat structure</b>
<p>A special internal spot
in which Perl keeps the information about the last <b>file</b> on which you
requested information.</p>
</li>
<li><a name="status"></a><b>status</b>
<p>The <b>value</b> returned to the
parent <b>process</b> when one of its child processes dies. This value is
placed in the special variable <code class="inline"><span class="i">$?</span></code>
. Its upper eight <b>bits</b> are the exit
status of the defunct process, and its lower eight bits identify the signal
(if any) that the process died from. On Unix systems, this status value is
the same as the status word returned by <i>wait</i>(2). See <code class="inline"><a class="l_k" href="functions/system.html">system</a></code> in Camel
chapter 27, &#x201c;Functions&#x201d;.</p>
</li>
<li><a name="STDERR"></a><b>STDERR</b>
<p>See <b>standard error</b>.</p>
</li>
<li><a name="STDIN"></a><b>STDIN</b>
<p>See <b>standard input</b>.</p>
</li>
<li><a name="STDIO"></a><b>STDIO</b>
<p>See <b>standard I/O</b>.</p>
</li>
<li><a name="STDOUT"></a><b>STDOUT</b>
<p>See <b>standard output</b>.</p>
</li>
<li><a name="stream"></a><b>stream</b>
<p>A flow of data into or out of
a process as a steady sequence of bytes or characters, without the
appearance of being broken up into packets. This is a kind of
<b>interface</b>&#x2014;the underlying <b>implementation</b> may well break your data up
into separate packets for delivery, but this is hidden from you.</p>
</li>
<li><a name="string"></a><b>string</b>
<p>A sequence of characters such as &#x201c;He said !@#*&amp;%@#*?!&#x201d;.
A string does not have to be entirely printable.</p>
</li>
<li><a name="string-context"></a><b>string context</b>
<p>The situation in which an expression is
expected by its surroundings (the code calling it) to return a <b>string</b>.
See also <b>context</b> and <b>numeric context</b>.</p>
</li>
<li><a name="stringification"></a><b>stringification</b>
<p>The process of producing a <b>string</b> representation of an
abstract object.</p>
</li>
<li><a name="struct"></a><b>struct</b>
<p>C keyword introducing a structure definition or name.</p>
</li>
<li><a name="structure"></a><b>structure</b>
<p>See <b>data structure</b>.</p>
</li>
<li><a name="subclass"></a><b>subclass</b>
<p>See <b>derived class</b>.</p>
</li>
<li><a name="subpattern"></a><b>subpattern</b>
<p>A component of a <b>regular expression</b> pattern.</p>
</li>
<li><a name="subroutine"></a><b>subroutine</b>
<p>A named or otherwise accessible piece of program
that can be invoked from elsewhere in the program in order to accomplish
some subgoal of the program. A subroutine is often parameterized to
accomplish different but related things depending on its input
<b>arguments</b>. If the subroutine returns a meaningful <b>value</b>, it is also
called a <b>function</b>.</p>
</li>
<li><a name="subscript"></a><b>subscript</b>
<p>A <b>value</b> that indicates the position of a particular
<b>array</b> <b>element</b> in an array.</p>
</li>
<li><a name="substitution"></a><b>substitution</b>
<p>Changing parts of a string via the <code class="inline"><a class="l_k" href="functions/s.html">s///</a></code>
operator. (We avoid use of this term to mean <b>variable interpolation</b>.)</p>
</li>
<li><a name="substring"></a><b>substring</b>
<p>A portion of a <b>string</b>, starting at a certain
<b>character</b> position (<b>offset</b>) and proceeding for a certain number of
characters.</p>
</li>
<li><a name="superclass"></a><b>superclass</b>
<p>See <b>base class</b>.</p>
</li>
<li><a name="superuser"></a><b>superuser</b>
<p>The person whom the <b>operating system</b> will let do almost
anything. Typically your system administrator or someone pretending to be
your system administrator. On Unix systems, the <b>root</b> user. On Windows
systems, usually the Administrator user.</p>
</li>
<li><a name="SV"></a><b>SV</b>
<p>Short for &#x201c;scalar value&#x201d;. But
within the Perl interpreter, every <b>referent</b> is treated as a member of a
class derived from SV, in an object-oriented sort of way. Every <b>value</b>
inside Perl is passed around as a C language <code class="inline"><span class="w">SV</span>*</code>
 pointer. The SV
<b>struct</b> knows its own &#x201c;referent type&#x201d;, and the code is smart enough (we
hope) not to try to call a <b>hash</b> function on a <b>subroutine</b>.</p>
</li>
<li><a name="switch"></a><b>switch</b>
<p>An option you give on a command line to
influence the way your program works, usually introduced with a minus sign.
The word is also used as a nickname for a <b>switch statement</b>.</p>
</li>
<li><a name="switch-cluster"></a><b>switch cluster</b>
<p>The combination of multiple command-
line switches (<i>e.g.</i>, <code class="inline"><span class="q">&ndash;a &ndash;b &ndash;c</span></code>
) into one switch (<i>e.g.</i>, <code class="inline"><span class="q">&ndash;abc</span></code>
).
Any switch with an additional <b>argument</b> must be the last switch in a
cluster.</p>
</li>
<li><a name="switch-statement"></a><b>switch statement</b>
<p>A program technique that lets you
evaluate an <b>expression</b> and then, based on the value of the expression,
do a multiway branch to the appropriate piece of code for that value. Also
called a &#x201c;case structure&#x201d;, named after the similar Pascal construct. Most
switch statements in Perl are spelled <code class="inline">given</code>
. See &#x201c;The <code class="inline">given</code>

statement&#x201d; in Camel chapter 4, &#x201c;Statements and Declarations&#x201d;.</p>
</li>
<li><a name="symbol"></a><b>symbol</b>
<p>Generally, any <b>token</b> or <b>metasymbol</b>. Often used
more specifically to mean the sort of name you might find in a <b>symbol
table</b>.</p>
</li>
<li><a name="symbolic-debugger"></a><b>symbolic debugger</b>
<p>A program that lets you step through
the <b>execution</b> of your program, stopping or printing things out here and
there to see whether anything has gone wrong, and, if so, what. The
&#x201c;symbolic&#x201d; part just means that you can talk to the debugger using the same
symbols with which your program is written.</p>
</li>
<li><a name="symbolic-link"></a><b>symbolic link</b>
<p>An alternate filename that points to the
real <b>filename</b>, which in turn points to the real <b>file</b>. Whenever the
<b>operating system</b> is trying to parse a <b>pathname</b> containing a symbolic
link, it merely substitutes the new name and continues parsing.</p>
</li>
<li><a name="symbolic-reference"></a><b>symbolic reference</b>
<p>A variable whose value is the
name of another variable or subroutine. By <b>dereferencing</b> the first
variable, you can get at the second one. Symbolic references are illegal
under <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&quot;refs&quot;</span></code>
.</p>
</li>
<li><a name="symbol-table"></a><b>symbol table</b>
<p>Where a <b>compiler</b> remembers symbols. A program
like Perl must somehow remember all the names of all the <b>variables</b>,
<b>filehandles</b>, and <b>subroutines</b> you&#x2019;ve used. It does this by placing the
names in a symbol table, which is implemented in Perl using a <b>hash
table</b>. There is a separate symbol table for each <b>package</b> to give each
package its own <b>namespace</b>.</p>
</li>
<li><a name="synchronous"></a><b>synchronous</b>
<p>Programming in which the orderly sequence of events
can be determined; that is, when things happen one after the other, not at
the same time.</p>
</li>
<li><a name="syntactic-sugar"></a><b>syntactic sugar</b>
<p>An alternative way of writing something more easily; a
shortcut.</p>
</li>
<li><a name="syntax"></a><b>syntax</b>
<p>From Greek &#x3c3;&#x3cd;&#x3bd;&#x3c4;&#x3b1;&#x3be;&#x3b9;&#x3c2;, &#x201c;with-arrangement&#x201d;. How things
(particularly symbols) are put together with each other.</p>
</li>
<li><a name="syntax-tree"></a><b>syntax tree</b>
<p>An internal representation of your program wherein
lower-level <b>constructs</b> dangle off the higher-level constructs enclosing
them.</p>
</li>
<li><a name="syscall"></a><b>syscall</b>
<p>A <b>function</b> call directly to the <b>operating
system</b>. Many of the important subroutines and functions you use aren&#x2019;t
direct system calls, but are built up in one or more layers above the
system call level. In general, Perl programmers don&#x2019;t need to worry about
the distinction. However, if you do happen to know which Perl functions are
really syscalls, you can predict which of these will set the <code class="inline"><span class="i">$!</span></code>

(<code class="inline"><span class="i">$ERRNO</span></code>
) variable on failure. Unfortunately, beginning programmers often
confusingly employ the term &#x201c;system call&#x201d; to mean what happens when you
call the Perl <code class="inline"><a class="l_k" href="functions/system.html">system</a></code> function, which actually involves many syscalls. To
avoid any confusion, we nearly always say &#x201c;syscall&#x201d; for something you could
call indirectly via Perl&#x2019;s <code class="inline"><a class="l_k" href="functions/syscall.html">syscall</a></code> function, and never for something you
would call with Perl&#x2019;s <code class="inline"><a class="l_k" href="functions/system.html">system</a></code> function.</p>
</li>
</ul>
<a name="T"></a><h2>T</h2>
<ul>
<li><a name="taint-checks"></a><b>taint checks</b>
<p>The special bookkeeping Perl does to track the flow
of external data through your program and disallow their use in system
commands.</p>
</li>
<li><a name="tainted"></a><b>tainted</b>
<p>Said of data derived from the grubby hands of a user,
and thus unsafe for a secure program to rely on. Perl does taint checks if
you run a <b>setuid</b> (or <b>setgid</b>) program, or if you use the <code class="inline"><span class="q">&ndash;T</span></code>
 switch.</p>
</li>
<li><a name="taint-mode"></a><b>taint mode</b>
<p>Running under the <code class="inline"><span class="q">&ndash;T</span></code>
 switch, marking all external data as
suspect and refusing to use it with system commands. See Camel chapter 20,
&#x201c;Security&#x201d;.</p>
</li>
<li><a name="TCP"></a><b>TCP</b>
<p>Short for Transmission Control Protocol. A protocol wrapped around the
Internet Protocol to make an unreliable packet transmission mechanism
appear to the application program to be a reliable <b>stream</b> of bytes.
(Usually.)</p>
</li>
<li><a name="term"></a><b>term</b>
<p>Short for a &#x201c;terminal&#x201d;&#x2014;that is, a leaf node of a <b>syntax
tree</b>. A thing that functions grammatically as an <b>operand</b> for the
operators in an expression.</p>
</li>
<li><a name="terminator"></a><b>terminator</b>
<p>A <b>character</b> or <b>string</b> that marks the end of another string. The <code class="inline"><span class="i">$/</span></code>

variable contains the string that terminates a <code class="inline"><a class="l_k" href="functions/readline.html">readline</a></code> operation, which
<code class="inline"><a class="l_k" href="functions/chomp.html">chomp</a></code> deletes from the end. Not to be confused with <b>delimiters</b> or
<b>separators</b>. The period at the end of this sentence is a terminator.</p>
</li>
<li><a name="ternary"></a><b>ternary</b>
<p>An <b>operator</b> taking three <b>operands</b>. Sometimes
pronounced <b>trinary</b>.</p>
</li>
<li><a name="text"></a><b>text</b>
<p>A <b>string</b> or <b>file</b> containing primarily printable characters.</p>
</li>
<li><a name="thread"></a><b>thread</b>
<p>Like a forked process, but without <b>fork</b>&#x2019;s inherent
memory protection. A thread is lighter weight than a full process, in that
a process could have multiple threads running around in it, all fighting
over the same process&#x2019;s memory space unless steps are taken to protect
threads from one another.</p>
</li>
<li><a name="tie"></a><b>tie</b>
<p>The bond between a magical variable and its
implementation class. See the <code class="inline"><a class="l_k" href="functions/tie.html">tie</a></code> function in Camel chapter 27,
&#x201c;Functions&#x201d; and Camel chapter 14, &#x201c;Tied Variables&#x201d;.</p>
</li>
<li><a name="titlecase"></a><b>titlecase</b>
<p>The case used for capitals
that are followed by lowercase characters instead of by more capitals.
Sometimes called sentence case or headline case. English doesn&#x2019;t use
Unicode titlecase, but casing rules for English titles are more complicated
than simply capitalizing each word&#x2019;s first character.</p>
</li>
<li><a name="TMTOWTDI"></a><b>TMTOWTDI</b>
<p>There&#x2019;s More Than One Way To Do It, the Perl Motto. The
notion that there can be more than one valid path to solving a programming
problem in context. (This doesn&#x2019;t mean that more ways are always better or
that all possible paths are equally desirable&#x2014;just that there need not be
One True Way.)</p>
</li>
<li><a name="token"></a><b>token</b>
<p>A morpheme in a programming language, the smallest unit
of text with semantic significance.</p>
</li>
<li><a name="tokener"></a><b>tokener</b>
<p>A module that breaks a program text into a sequence of
<b>tokens</b> for later analysis by a parser.</p>
</li>
<li><a name="tokenizing"></a><b>tokenizing</b>
<p>Splitting up a program text into <b>tokens</b>. Also known as
&#x201c;lexing&#x201d;, in which case you get &#x201c;lexemes&#x201d; instead of tokens.</p>
</li>
<li><a name="toolbox-approach"></a><b>toolbox approach</b>
<p>The notion that, with a complete set of simple tools
that work well together, you can build almost anything you want. Which is
fine if you&#x2019;re assembling a tricycle, but if you&#x2019;re building a
defranishizing comboflux regurgalator, you really want your own machine
shop in which to build special tools. Perl is sort of a machine shop.</p>
</li>
<li><a name="topic"></a><b>topic</b>
<p>The thing you&#x2019;re working on. Structures like
<code class="inline"><a class="l_k" href="functions/while.html">while(<>)</a></code>, <code class="inline">for</code>
, <code class="inline">foreach</code>
, and <code class="inline">given</code>
 set the topic for
you by assigning to <code class="inline"><span class="i">$_</span></code>
, the default (<i>topic</i>) variable.</p>
</li>
<li><a name="transliterate"></a><b>transliterate</b>
<p>To turn one string
representation into another by mapping each character of the source string
to its corresponding character in the result string. Not to be confused
with translation: for example, Greek <i>&#x3c0;&#x3bf;&#x3bb;&#x3cd;&#x3c7;&#x3c1;&#x3c9;&#x3bc;&#x3bf;&#x3c2;</i> transliterates into
<i>polychromos</i> but translates into <i>many-colored</i>. See the <code class="inline"><a class="l_k" href="functions/tr.html">tr///</a></code>
operator in Camel chapter 5, &#x201c;Pattern Matching&#x201d;.</p>
</li>
<li><a name="trigger"></a><b>trigger</b>
<p>An event that causes a <b>handler</b> to be run.</p>
</li>
<li><a name="trinary"></a><b>trinary</b>
<p>Not a stellar system with three stars, but an
<b>operator</b> taking three <b>operands</b>. Sometimes pronounced <b>ternary</b>.</p>
</li>
<li><a name="troff"></a><b>troff</b>
<p>A venerable typesetting language from which Perl derives
the name of its <code class="inline"><span class="i">$%</span></code>
 variable and which is secretly used in the production
of Camel books.</p>
</li>
<li><a name="true"></a><b>true</b>
<p>Any scalar value that doesn&#x2019;t evaluate to 0 or
<code class="inline"><span class="q">&quot;&quot;</span></code>
.</p>
</li>
<li><a name="truncating"></a><b>truncating</b>
<p>Emptying a file of existing
contents, either automatically when opening a file for writing or
explicitly via the <code class="inline"><a class="l_k" href="functions/truncate.html">truncate</a></code> function.</p>
</li>
<li><a name="type"></a><b>type</b>
<p>See <b>data type</b> and <b>class</b>.</p>
</li>
<li><a name="type-casting"></a><b>type casting</b>
<p>Converting data from one type to another. C permits this.
Perl does not need it. Nor want it.</p>
</li>
<li><a name="typedef"></a><b>typedef</b>
<p>A type definition in the C and C++ languages.</p>
</li>
<li><a name="typed-lexical"></a><b>typed lexical</b>
<p>A <b>lexical variable</b>  lexical&gt;that is declared with a <b>class</b>
type: <code class="inline"><a class="l_k" href="functions/my.html">my</a> <span class="w">Pony</span> <span class="i">$bill</span></code>
.</p>
</li>
<li><a name="typeglob"></a><b>typeglob</b>
<p>Use of a single identifier, prefixed with <code class="inline"><span class="i">*</span></code>
. For
example, <code class="inline"><span class="i">*name</span></code>
 stands for any or all of <code class="inline"><span class="i">$name</span></code>
, <code class="inline"><span class="i">@name</span></code>
, <code class="inline"><span class="i">%name</span></code>
,
<code class="inline"><span class="i">&amp;name</span></code>
, or just <code class="inline"><span class="w">name</span></code>
. How you use it determines whether it is
interpreted as all or only one of them. See &#x201c;Typeglobs and Filehandles&#x201d; in
Camel chapter 2, &#x201c;Bits and Pieces&#x201d;.</p>
</li>
<li><a name="typemap"></a><b>typemap</b>
<p>A description of how C types may be transformed to and from Perl
types within an <b>extension</b> module written in <b>XS</b>.</p>
</li>
</ul>
<a name="U"></a><h2>U</h2>
<ul>
<li><a name="UDP"></a><b>UDP</b>
<p>User Datagram Protocol, the typical way to send
<b>datagrams</b> over the Internet.</p>
</li>
<li><a name="UID"></a><b>UID</b>
<p>A user ID. Often used in the context of
<b>file</b> or <b>process</b> ownership.</p>
</li>
<li><a name="umask"></a><b>umask</b>
<p>A mask of those <b>permission bits</b> that should be forced
off when creating files or directories, in order to establish a policy of
whom you&#x2019;ll ordinarily deny access to. See the <code class="inline"><a class="l_k" href="functions/umask.html">umask</a></code> function.</p>
</li>
<li><a name="unary-operator"></a><b>unary operator</b>
<p>An operator with only one <b>operand</b>, like <code class="inline">!</code>
 or
<code class="inline"><a class="l_k" href="functions/chdir.html">chdir</a></code>. Unary operators are usually prefix operators; that is, they
precede their operand. The <code class="inline">++</code>
 and <code class="inline"><span class="q">&ndash;&ndash;</span></code>
 operators can be either prefix
or postfix. (Their position <i>does</i> change their meanings.)</p>
</li>
<li><a name="Unicode"></a><b>Unicode</b>
<p>A character set comprising all the major character sets of
the world, more or less. See <a href="http://www.unicode.org">http://www.unicode.org</a>.</p>
</li>
<li><a name="Unix"></a><b>Unix</b>
<p>A very large and constantly evolving language with several
alternative and largely incompatible syntaxes, in which anyone can define
anything any way they choose, and usually do. Speakers of this language
think it&#x2019;s easy to learn because it&#x2019;s so easily twisted to one&#x2019;s own ends,
but dialectical differences make tribal intercommunication nearly
impossible, and travelers are often reduced to a pidgin-like subset of the
language. To be universally understood, a Unix shell programmer must spend
years of study in the art. Many have abandoned this discipline and now
communicate via an Esperanto-like language called Perl.</p>
<p>In ancient times, Unix was also used to refer to some code that a couple of
people at Bell Labs wrote to make use of a PDP-7 computer that wasn&#x2019;t doing
much of anything else at the time.</p>
</li>
<li><a name="uppercase"></a><b>uppercase</b>
<p>In Unicode, not just
characters with the General Category of Uppercase Letter, but any character
with the Uppercase property, including some Letter Numbers and Symbols. Not
to be confused with <b>titlecase</b>.</p>
</li>
</ul>
<a name="V"></a><h2>V</h2>
<ul>
<li><a name="value"></a><b>value</b>
<p>An actual piece of data, in contrast to all the
variables, references, keys, indices, operators, and whatnot that you need
to access the value.</p>
</li>
<li><a name="variable"></a><b>variable</b>
<p>A named storage location that can hold any
of various kinds of <b>value</b>, as your program sees fit.</p>
</li>
<li><a name="variable-interpolation"></a><b>variable interpolation</b>
<p>The <b>interpolation</b> of
a scalar or array variable into a string.</p>
</li>
<li><a name="variadic"></a><b>variadic</b>
<p>Said of a <b>function</b> that happily receives an
indeterminate number of <b>actual arguments</b>.</p>
</li>
<li><a name="vector"></a><b>vector</b>
<p>Mathematical jargon for a list of <b>scalar values</b>.</p>
</li>
<li><a name="virtual"></a><b>virtual</b>
<p>Providing the appearance of something without the reality,
as in: virtual memory is not real memory. (See also <b>memory</b>.) The
opposite of &#x201c;virtual&#x201d; is &#x201c;transparent&#x201d;, which means providing the reality
of something without the appearance, as in: Perl handles the
variable-length UTF&#x2011;8 character encoding transparently.</p>
</li>
<li><a name="void-context"></a><b>void context</b>
<p>A form of <b>scalar context</b> in which an
<b>expression</b> is not expected to return any <b>value</b> at all and is
evaluated for its <b>side effects</b> alone.</p>
</li>
<li><a name="v-string"></a><b>v-string</b>
<p>A &#x201c;version&#x201d; or &#x201c;vector&#x201d; <b>string</b>
specified with a <code class="inline"><span class="w">v</span></code>
 followed by a series of decimal integers in dot
notation, for instance, <code class="inline"><span class="v">v1.20.300.4000</span></code>
. Each number turns into a
<b>character</b> with the specified ordinal value. (The <code class="inline"><span class="w">v</span></code>
 is optional when
there are at least three integers.)</p>
</li>
</ul>
<a name="W"></a><h2>W</h2>
<ul>
<li><a name="warning"></a><b>warning</b>
<p>A message printed to the <code class="inline"><span class="w">STDERR</span></code>
 stream to the effect that something might be
wrong but isn&#x2019;t worth blowing up over. See <code class="inline"><a class="l_k" href="functions/warn.html">warn</a></code> in Camel chapter 27,
&#x201c;Functions&#x201d; and the <code class="inline"><span class="w">warnings</span></code>
 pragma in Camel chapter 28, &#x201c;Pragmantic
Modules&#x201d;.</p>
</li>
<li><a name="watch-expression"></a><b>watch expression</b>
<p>An expression which, when its value
changes, causes a breakpoint in the Perl debugger.</p>
</li>
<li><a name="weak-reference"></a><b>weak reference</b>
<p>A reference that doesn&#x2019;t get counted
normally. When all the normal references to data disappear, the data
disappears. These are useful for circular references that would never
disappear otherwise.</p>
</li>
<li><a name="whitespace"></a><b>whitespace</b>
<p>A <b>character</b> that moves
your cursor but doesn&#x2019;t otherwise put anything on your screen. Typically
refers to any of: space, tab, line feed, carriage return, or form feed. In
Unicode, matches many other characters that Unicode considers whitespace,
including the &#x274;-&#x299;&#x280; .</p>
</li>
<li><a name="word"></a><b>word</b>
<p>In normal &#x201c;computerese&#x201d;, the piece of data of the size most
efficiently handled by your computer, typically 32 bits or so, give or take a
few powers of 2. In Perl culture, it more often refers to an alphanumeric
<b>identifier</b> (including underscores), or to a string of nonwhitespace
<b>characters</b> bounded by whitespace or string boundaries.</p>
</li>
<li><a name="working-directory"></a><b>working directory</b>
<p>Your current <b>directory</b>, from
which relative pathnames are interpreted by the <b>operating system</b>. The
operating system knows your current directory because you told it with a
<code class="inline"><a class="l_k" href="functions/chdir.html">chdir</a></code>, or because you started out in the place where your parent
<b>process</b> was when you were born.</p>
</li>
<li><a name="wrapper"></a><b>wrapper</b>
<p>A program or subroutine that runs some other program or
subroutine for you, modifying some of its input or output to better suit
your purposes.</p>
</li>
<li><a name="WYSIWYG"></a><b>WYSIWYG</b>
<p>What You See Is What You Get. Usually used when something
that appears on the screen matches how it will eventually look, like Perl&#x2019;s
<code class="inline"><a class="l_k" href="functions/format.html">format</a></code> declarations. Also used to mean the opposite of magic because
everything works exactly as it appears, as in the three- argument form of
<code class="inline"><a class="l_k" href="functions/open.html">open</a></code>.</p>
</li>
</ul>
<a name="X"></a><h2>X</h2>
<ul>
<li><a name="XS"></a><b>XS</b>
<p>An extraordinarily
exported, expeditiously excellent, expressly eXternal Subroutine, executed
in existing C or C++ or in an exciting extension language called
(exasperatingly) XS.</p>
</li>
<li><a name="XSUB"></a><b>XSUB</b>
<p>An external <b>subroutine</b> defined in <b>XS</b>.</p>
</li>
</ul>
<a name="Y"></a><h2>Y</h2>
<ul>
<li><a name="yacc"></a><b>yacc</b>
<p>Yet Another Compiler Compiler. A parser generator without
which Perl probably would not have existed. See the file <i>perly.y</i> in the
Perl source distribution.</p>
</li>
</ul>
<a name="Z"></a><h2>Z</h2>
<ul>
<li><a name="zero-width"></a><b>zero width</b>
<p>A subpattern <b>assertion</b> matching the <b>null
string</b> between <b>characters</b>.</p>
</li>
<li><a name="zombie"></a><b>zombie</b>
<p>A process that has died (exited) but
whose parent has not yet received proper notification of its demise by
virtue of having called <code class="inline"><a class="l_k" href="functions/wait.html">wait</a></code> or <code class="inline"><a class="l_k" href="functions/waitpid.html">waitpid</a></code>. If you <code class="inline"><a class="l_k" href="functions/fork.html">fork</a></code>, you must
clean up after your child processes when they exit; otherwise, the process
table will fill up and your system administrator will Not Be Happy with
you.</p>
</li>
</ul>
<a name="AUTHOR-AND-COPYRIGHT"></a><h1>AUTHOR AND COPYRIGHT</h1>
<p>Based on the Glossary of <i>Programming Perl</i>, Fourth Edition,
by Tom Christiansen, brian d foy, Larry Wall, &amp; Jon Orwant.
Copyright (c) 2000, 1996, 1991, 2012 O'Reilly Media, Inc.
This document may be distributed under the same terms as Perl itself.</p>




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