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            <h1>perlreref</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#OPERATORS">OPERATORS</a><li><a href="#SYNTAX">SYNTAX</a><li><a href="#ESCAPE-SEQUENCES">ESCAPE SEQUENCES</a><li><a href="#CHARACTER-CLASSES">CHARACTER CLASSES</a><li><a href="#ANCHORS">ANCHORS</a><li><a href="#QUANTIFIERS">QUANTIFIERS</a><li><a href="#EXTENDED-CONSTRUCTS">EXTENDED CONSTRUCTS</a><li><a href="#VARIABLES">VARIABLES</a><li><a href="#FUNCTIONS">FUNCTIONS</a><li><a href="#TERMINOLOGY">TERMINOLOGY</a></ul><li><a href="#AUTHOR">AUTHOR</a><li><a href="#SEE-ALSO">SEE ALSO</a><li><a href="#THANKS">THANKS</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>perlreref - Perl Regular Expressions Reference</p>
<a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>This is a quick reference to Perl's regular expressions.
For full information see <a href="perlre.html">perlre</a> and <a href="perlop.html">perlop</a>, as well
as the <a href="#SEE-ALSO">SEE ALSO</a> section in this document.</p>
<a name="OPERATORS"></a><h2>OPERATORS</h2>
<p><code class="inline">=~</code>
 determines to which variable the regex is applied.
In its absence, $_ is used.</p>
<pre class="verbatim"><ol><li>    <span class="i">$var</span> =~ <span class="q">/foo/</span><span class="sc">;</span></li></ol></pre><p><code class="inline">!~</code>
 determines to which variable the regex is applied,
and negates the result of the match; it returns
false if the match succeeds, and true if it fails.</p>
<pre class="verbatim"><ol><li>    <span class="i">$var</span> !~ <span class="q">/foo/</span><span class="sc">;</span></li></ol></pre><p><code class="inline"><a class="l_k" href="functions/m.html">m/pattern/msixpogcdualn</a></code> searches a string for a pattern match,
applying the given options.</p>
<pre class="verbatim"><ol><li>    <span class="q">m  Multiline mode - ^ and $ match internal lines</span></li><li>    <span class="q">    s  match as a Single line - . matches \n</span></li><li>    <span class="q">    i  case-Insensitive</span></li><li>    <span class="q">    x  eXtended legibility - free whitespace and comments</span></li><li>    <span class="q">    p  Preserve a copy of the matched string -</span></li><li>       <span class="q">       ${^PREMATCH</span><span class="s">}</span><span class="cm">,</span> <span class="i">$</span>{<span class="w">^MATCH</span>}<span class="cm">,</span> <span class="i">$</span>{<span class="w">^POSTMATCH</span>} <span class="w">will</span> <span class="w">be</span> <a class="l_k" href="functions/defined.html">defined</a>.</li><li>    <span class="w">o</span>  <span class="w">compile</span> <span class="w">pattern</span> <span class="w">Once</span></li><li>    <span class="w">g</span>  <span class="w">Global</span> - <span class="w">all</span> <span class="w">occurrences</span></li><li>    <span class="w">c</span>  <span class="w">don&#39;t</span> <a class="l_k" href="functions/reset.html">reset</a> <a class="l_k" href="functions/pos.html">pos</a> <span class="w">on</span> <span class="w">failed</span> <span class="w">matches</span> <a class="l_k" href="functions/when.html">when</a> <span class="w">using</span> /<span class="w">g</span></li><li>    <span class="w">a</span>  <span class="w">restrict</span> \<span class="w">d</span><span class="cm">,</span> \<span class="q">s, \w and [:posix:] to match ASCII only</span></li><li>    <span class="q">    aa (two a&#39;s) also /i matches exclude ASCII/non-ASCII</span></li><li>    <span class="q">    l  match according to current locale</span></li><li>    <span class="q">    u  match according to Unicode rules</span></li><li>    <span class="q">    d  match according to native rules unless something indicates</span></li><li>       <span class="q">       Unicode</span></li><li>    <span class="q">    n  Non-capture mode. Don&#39;t let () fill in $1, $2,</span> <span class="w">etc</span>...</li></ol></pre><p>If 'pattern' is an empty string, the last <i>successfully</i> matched
regex is used. Delimiters other than '/' may be used for both this
operator and the following ones. The leading <code class="inline"><a class="l_k" href="functions/m.html">m</a></code> can be omitted
if the delimiter is '/'.</p>
<p><code class="inline"><a class="l_k" href="functions/qr.html">qr/pattern/msixpodualn</a></code> lets you store a regex in a variable,
or pass one around. Modifiers as for <code class="inline"><a class="l_k" href="functions/m.html">m//</a></code>, and are stored
within the regex.</p>
<p><code class="inline"><a class="l_k" href="functions/s.html">s/pattern/replacement/msixpogcedual</a></code> substitutes matches of
'pattern' with 'replacement'. Modifiers as for <code class="inline"><a class="l_k" href="functions/m.html">m//</a></code>,
with two additions:</p>
<pre class="verbatim"><ol><li>    <span class="w">e</span>  <span class="w">Evaluate</span> <span class="q">&#39;replacement&#39;</span> <span class="w">as</span> <span class="w">an</span> <span class="w">expression</span></li><li>    <span class="w">r</span>  <span class="w">Return</span> <span class="w">substitution</span> and <span class="w">leave</span> <span class="w">the</span> <span class="w">original</span> <span class="w">string</span> <span class="w">untouched</span>.</li></ol></pre><p>'e' may be specified multiple times. 'replacement' is interpreted
as a double quoted string unless a single-quote (<code class="inline">'</code>) is the delimiter.</p>
<p><code class="inline"><a class="l_k" href="functions/m.html">m?pattern?</a></code> is like <code class="inline"><a class="l_k" href="functions/m.html">m/pattern/</a></code> but matches only once. No alternate
delimiters can be used.  Must be reset with reset().</p>
<a name="SYNTAX"></a><h2>SYNTAX</h2>
<pre class="verbatim"><ol><li> \       <span class="w">Escapes</span> <span class="w">the</span> <span class="w">character</span> <span class="w">immediately</span> <span class="w">following</span> <span class="w">it</span></li><li> .       <span class="w">Matches</span> <span class="w">any</span> <span class="w">single</span> <span class="w">character</span> <span class="w">except</span> <span class="w">a</span> <span class="w">newline</span> <span class="s">(</span>unless <span class="q">/s is</span></li><li>           <span class="q">           used)</span></li><li> <span class="q"> ^       Matches at the beginning of the string (or line, if /m</span> <span class="w">is</span> <span class="w">used</span><span class="s">)</span></li><li> <span class="i">$       Matches</span> <span class="w">at</span> <span class="w">the</span> <span class="w">end</span> <span class="w">of</span> <span class="w">the</span> <span class="w">string</span> <span class="s">(</span>or <span class="w">line</span><span class="cm">,</span> if <span class="q">/m is used)</span></li><li> <span class="q"> *       Matches the preceding element 0 or more times</span></li><li> <span class="q"> +       Matches the preceding element 1 or more times</span></li><li> <span class="q"> ?       Matches the preceding element 0 or 1 times</span></li><li> <span class="q"> {...}   Specifies a range of occurrences for the element preceding it</span></li><li> <span class="q"> [...]   Matches any one of the characters contained within the brackets</span></li><li> <span class="q"> (...)   Groups subexpressions for capturing to $1, $2...</span></li><li> <span class="q"> (?:...) Groups subexpressions without capturing (cluster)</span></li><li> <span class="q"> |       Matches either the subexpression preceding or following it</span></li><li> <span class="q"> \g1 or \g{1}, \g2 ...    Matches the text from the Nth group</span></li><li> <span class="q"> \1, \2, \3 ...           Matches the text from the Nth group</span></li><li> <span class="q"> \g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group</span></li><li> <span class="q"> \g{name}     Named backreference</span></li><li> <span class="q"> \k&lt;name&gt;     Named backreference</span></li><li> <span class="q"> \k&#39;name&#39;     Named backreference</span></li><li> <span class="q"> (?P=name)    Named backreference (python syntax)</span></li></ol></pre><a name="ESCAPE-SEQUENCES"></a><h2>ESCAPE SEQUENCES</h2>
<p>These work as in normal strings.</p>
<pre class="verbatim"><ol><li>   \<span class="w">a</span>       <span class="w">Alarm</span> <span class="s">(</span><span class="w">beep</span><span class="s">)</span></li><li>   \<span class="w">e</span>       <span class="w">Escape</span></li><li>   \<span class="w">f</span>       <span class="w">Formfeed</span></li><li>   \<span class="w">n</span>       <span class="w">Newline</span></li><li>   \<span class="w">r</span>       <span class="w">Carriage</span> <a class="l_k" href="functions/return.html">return</a></li><li>   \<span class="w">t</span>       <span class="w">Tab</span></li><li>   \<span class="n">037</span>     <span class="w">Char</span> <span class="w">whose</span> <span class="w">ordinal</span> <span class="w">is</span> <span class="w">the</span> <span class="n">3</span> <span class="w">octal</span> <span class="w">digits</span><span class="cm">,</span> <span class="w">max</span> \<span class="n">777</span></li><li>   \<span class="i">o</span><span class="s">{</span><span class="n">2307</span><span class="s">}</span> <span class="w">Char</span> <span class="w">whose</span> <span class="w">ordinal</span> <span class="w">is</span> <span class="w">the</span> <span class="w">octal</span> <span class="w">number</span><span class="cm">,</span> <span class="w">unrestricted</span></li><li>   \<span class="w">x7f</span>     <span class="w">Char</span> <span class="w">whose</span> <span class="w">ordinal</span> <span class="w">is</span> <span class="w">the</span> <span class="n">2</span> <a class="l_k" href="functions/hex.html">hex</a> <span class="w">digits</span><span class="cm">,</span> <span class="w">max</span> \<span class="w">xFF</span></li><li>   \<span class="i">x</span><span class="s">{</span><span class="n">263</span><span class="w">a</span><span class="s">}</span> <span class="w">Char</span> <span class="w">whose</span> <span class="w">ordinal</span> <span class="w">is</span> <span class="w">the</span> <a class="l_k" href="functions/hex.html">hex</a> <span class="w">number</span><span class="cm">,</span> <span class="w">unrestricted</span></li><li>   \<span class="w">cx</span>      <span class="w">Control</span>-x</li><li>   \<span class="i">N</span><span class="s">{</span><span class="w">name</span><span class="s">}</span> <span class="w">A</span> <span class="w">named</span> <span class="w">Unicode</span> <span class="w">character</span> <a class="l_k" href="functions/or.html">or</a> <span class="w">character</span> <span class="w">sequence</span></li><li>   \<span class="i">N</span><span class="s">{</span><span class="w">U</span>+<span class="n">263</span><span class="w">D</span><span class="s">}</span> <span class="w">A</span> <span class="w">Unicode</span> <span class="w">character</span> <span class="w">by</span> <a class="l_k" href="functions/hex.html">hex</a> <span class="w">ordinal</span></li><li></li><li>   \<span class="w">l</span>  <span class="w">Lowercase</span> <a class="l_k" href="functions/next.html">next</a> <span class="j">character</span></li><li>   \<span class="w">u</span>  <span class="w">Titlecase</span> <a class="l_k" href="functions/next.html">next</a> <span class="j">character</span></li><li>   \<span class="w">L</span>  <span class="w">Lowercase</span> <a class="l_k" href="functions/until.html">until</a> \<span class="w">E</span></li><li>   \<span class="w">U</span>  <span class="w">Uppercase</span> <a class="l_k" href="functions/until.html">until</a> \<span class="w">E</span></li><li>   \<span class="w">F</span>  <span class="w">Foldcase</span> <a class="l_k" href="functions/until.html">until</a> \<span class="w">E</span></li><li>   \<span class="w">Q</span>  <span class="w">Disable</span> <span class="w">pattern</span> <span class="w">metacharacters</span> <a class="l_k" href="functions/until.html">until</a> \<span class="w">E</span></li><li>   \<span class="w">E</span>  <span class="w">End</span> <span class="w">modification</span></li></ol></pre><p>For Titlecase, see <a href="#Titlecase">Titlecase</a>.</p>
<p>This one works differently from normal strings:</p>
<pre class="verbatim"><ol><li>   \<span class="w">b</span>  <span class="w">An</span> <span class="w">assertion</span><span class="cm">,</span> not <span class="w">backspace</span><span class="cm">,</span> <span class="w">except</span> <span class="w">in</span> <span class="w">a</span> <span class="w">character</span> <span class="w">class</span></li></ol></pre><a name="CHARACTER-CLASSES"></a><h2>CHARACTER CLASSES</h2>
<pre class="verbatim"><ol><li>   [amy]    Match 'a', 'm' or 'y'</li><li>   [f-j]    Dash specifies "range"</li><li>   [f-j-]   Dash escaped or at start or end means 'dash'</li><li>   [^f-j]   Caret indicates "match any character _except_ these"</li></ol></pre><p>The following sequences (except <code class="inline">\<span class="w">N</span></code>
) work within or without a character class.
The first six are locale aware, all are Unicode aware. See <a href="perllocale.html">perllocale</a>
and <a href="perlunicode.html">perlunicode</a> for details.</p>
<pre class="verbatim"><ol><li>   \<span class="w">d</span>      <span class="w">A</span> <span class="w">digit</span></li><li>   \<span class="w">D</span>      <span class="w">A</span> <span class="w">nondigit</span></li><li>   \<span class="w">w</span>      <span class="w">A</span> <span class="w">word</span> <span class="w">character</span></li><li>   \<span class="w">W</span>      <span class="w">A</span> <span class="w">non</span>-<span class="w">word</span> <span class="w">character</span></li><li>   \<span class="q">s      A whitespace character</span></li><li>   <span class="q">   \S      A non-whitespace character</span></li><li>   <span class="q">   \h      An</span> <span class="w">horizontal</span> <span class="w">whitespace</span></li><li>   \<span class="w">H</span>      <span class="w">A</span> <span class="w">non</span> <span class="w">horizontal</span> <span class="w">whitespace</span></li><li>   \<span class="w">N</span>      <span class="w">A</span> <span class="w">non</span> <span class="w">newline</span> <span class="s">(</span><a class="l_k" href="functions/when.html">when</a> <a class="l_k" href="functions/not.html">not</a> <span class="w">followed</span> <span class="w">by</span> <span class="q">&#39;{NAME}&#39;</span><span class="sc">;</span><span class="sc">;</span></li><li>           <a class="l_k" href="functions/not.html">not</a> <span class="w">valid</span> <span class="w">in</span> <span class="w">a</span> <span class="w">character</span> <span class="w">class</span><span class="sc">;</span> <span class="w">equivalent</span> <span class="w">to</span> <span class="s">[</span>^\<span class="w">n</span><span class="s">]</span><span class="sc">;</span> <span class="w">it&#39;s</span></li><li>           <span class="w">like</span> <span class="q">&#39;.&#39;</span> <span class="w">without</span> /<span class="q">s modifier)</span></li><li>   <span class="q">   \v      A vertical whitespace</span></li><li>   <span class="q">   \V      A non vertical whitespace</span></li><li>   <span class="q">   \R      A generic newline           (?&gt;\v|\x0D\x0A)</span></li><li></li><li>   <span class="q">   \pP     Match P-named (Unicode) property</span></li><li>   <span class="q">   \p{...} Match Unicode property with name</span> <span class="w">longer</span> <span class="w">than</span> <span class="n">1</span> <span class="w">character</span></li><li>   \<span class="w">PP</span>     <span class="w">Match</span> <span class="w">non</span>-<span class="w">P</span></li><li>   \<span class="i">P</span><span class="s">{</span>...<span class="s">}</span> <span class="w">Match</span> <span class="w">lack</span> <span class="w">of</span> <span class="w">Unicode</span> <span class="w">property</span> <span class="w">with</span> <span class="w">name</span> <span class="w">longer</span> <span class="w">than</span> <span class="n">1</span> <span class="w">char</span></li><li>   \<span class="w">X</span>      <span class="w">Match</span> <span class="w">Unicode</span> <span class="w">extended</span> <span class="w">grapheme</span> <span class="w">cluster</span></li></ol></pre><p>POSIX character classes and their Unicode and Perl equivalents:</p>
<pre class="verbatim"><ol><li>            <span class="w">ASCII</span>-         <span class="w">Full</span>-</li><li>   <span class="w">POSIX</span>    <span class="w">range</span>          <span class="w">range</span>    <span class="w">backslash</span></li><li> <span class="s">[</span><span class="s">[</span><span class="co">:</span>...<span class="co">:</span><span class="s">]</span><span class="s">]</span>  \<span class="i">p</span><span class="s">{</span>...<span class="s">}</span>        \<span class="i">p</span><span class="s">{</span>...<span class="s">}</span>   <span class="w">sequence</span>    <span class="w">Description</span></li><li></li><li> -----------------------------------------------------------------------</li><li> <span class="w">alnum</span>   <span class="w">PosixAlnum</span>       <span class="w">XPosixAlnum</span>            <span class="q">&#39;alpha&#39;</span> <span class="w">plus</span> <span class="q">&#39;digit&#39;</span></li><li> <span class="w">alpha</span>   <span class="w">PosixAlpha</span>       <span class="w">XPosixAlpha</span>            <span class="w">Alphabetic</span> <span class="w">characters</span></li><li> <span class="w">ascii</span>   <span class="w">ASCII</span>                                   <span class="w">Any</span> <span class="w">ASCII</span> <span class="w">character</span></li><li> <span class="w">blank</span>   <span class="w">PosixBlank</span>       <span class="w">XPosixBlank</span>   \<span class="w">h</span>       <span class="w">Horizontal</span> <span class="w">whitespace</span><span class="sc">;</span></li><li>                                                   <span class="w">full</span>-<span class="w">range</span> <span class="w">also</span></li><li>                                                   <span class="w">written</span> <span class="w">as</span></li><li>                                                   \<span class="i">p</span><span class="s">{</span><span class="w">HorizSpace</span><span class="s">}</span> <span class="s">(</span><span class="w">GNU</span></li><li>                                                   <span class="w">extension</span><span class="s">)</span></li><li> <span class="w">cntrl</span>   <span class="w">PosixCntrl</span>       <span class="w">XPosixCntrl</span>            <span class="w">Control</span> <span class="w">characters</span></li><li> <span class="w">digit</span>   <span class="w">PosixDigit</span>       <span class="w">XPosixDigit</span>   \<span class="w">d</span>       <span class="w">Decimal</span> <span class="w">digits</span></li><li> <span class="w">graph</span>   <span class="w">PosixGraph</span>       <span class="w">XPosixGraph</span>            <span class="q">&#39;alnum&#39;</span> <span class="w">plus</span> <span class="q">&#39;punct&#39;</span></li><li> <span class="w">lower</span>   <span class="w">PosixLower</span>       <span class="w">XPosixLower</span>            <span class="w">Lowercase</span> <span class="w">characters</span></li><li> <a class="l_k" href="functions/print.html">print</a>   <span class="i">PosixPrint</span>       <span class="w">XPosixPrint</span>            <span class="q">&#39;graph&#39;</span> <span class="w">plus</span> <span class="q">&#39;space&#39;</span><span class="cm">,</span></li><li>                                                   <span class="w">but</span> <a class="l_k" href="functions/not.html">not</a> <span class="w">any</span> <span class="w">Controls</span></li><li> <span class="w">punct</span>   <span class="w">PosixPunct</span>       <span class="w">XPosixPunct</span>            <span class="w">Punctuation</span> <a class="l_k" href="functions/and.html">and</a> <span class="w">Symbols</span></li><li>                                                   <span class="w">in</span> <span class="w">ASCII</span>-<span class="w">range</span><span class="sc">;</span> <span class="w">just</span></li><li>                                                   <span class="w">punct</span> <span class="w">outside</span> <span class="w">it</span></li><li> <span class="w">space</span>   <span class="w">PosixSpace</span>       <span class="w">XPosixSpace</span>   \<span class="q">s       Whitespace</span></li><li> <span class="q"> upper   PosixUpper       XPosixUpper            Uppercase characters</span></li><li> <span class="q"> word    PosixWord        XPosixWord</span>    \<span class="w">w</span>       <span class="q">&#39;alnum&#39;</span> + <span class="w">Unicode</span> <span class="w">marks</span></li><li>                                                    + <span class="w">connectors</span><span class="cm">,</span> <span class="w">like</span></li><li>                                                    <span class="q">&#39;_&#39;</span> <span class="s">(</span><span class="w">Perl</span> <span class="w">extension</span><span class="s">)</span></li><li> <span class="w">xdigit</span>  <span class="w">ASCII_Hex_Digit</span>  <span class="w">XPosixDigit</span>            <span class="w">Hexadecimal</span> <span class="w">digit</span><span class="cm">,</span></li><li>                                                    <span class="w">ASCII</span>-<span class="w">range</span> <span class="w">is</span></li><li>                                                    <span class="s">[</span><span class="n">0</span>-<span class="n">9</span><span class="w">A</span>-<span class="w">Fa</span>-f<span class="s">]</span></li></ol></pre><p>Also, various synonyms like <code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">Alpha</span><span class="s">}</span></code>
 for <code class="inline">\<span class="i">p</span><span class="s">{</span><span class="w">XPosixAlpha</span><span class="s">}</span></code>
; all listed
in <a href="perluniprops.html#Properties-accessible-through-%5cp%7b%7d-and-%5cP%7b%7d">Properties accessible through \p{} and \P{} in perluniprops</a></p>
<p>Within a character class:</p>
<pre class="verbatim"><ol><li>    <span class="w">POSIX</span>      <span class="w">traditional</span>   <span class="w">Unicode</span></li><li>  <span class="s">[</span><span class="co">:</span><span class="w">digit</span><span class="co">:</span><span class="s">]</span>       \<span class="w">d</span>        \<span class="i">p</span><span class="s">{</span><span class="w">Digit</span><span class="s">}</span></li><li>  <span class="s">[</span><span class="co">:</span>^<span class="w">digit</span><span class="co">:</span><span class="s">]</span>      \<span class="w">D</span>        \<span class="i">P</span><span class="s">{</span><span class="w">Digit</span><span class="s">}</span></li></ol></pre><a name="ANCHORS"></a><h2>ANCHORS</h2>
<p>All are zero-width assertions.</p>
<pre class="verbatim"><ol><li>   ^  <span class="w">Match</span> <span class="w">string</span> <span class="w">start</span> <span class="s">(</span><a class="l_k" href="functions/or.html">or</a> <span class="w">line</span><span class="cm">,</span> <a class="l_k" href="functions/if.html">if</a> <span class="q">/m is used)</span></li><li>   <span class="q">   $  Match string end (or line, if /m</span> <span class="w">is</span> <span class="w">used</span><span class="s">)</span> <a class="l_k" href="functions/or.html">or</a> <span class="w">before</span> <span class="w">newline</span></li><li>   \<span class="w">b</span><span class="s">{</span><span class="s">}</span> <span class="w">Match</span> <span class="w">boundary</span> <span class="w">of</span> <span class="w">type</span> <span class="w">specified</span> <span class="w">within</span> <span class="w">the</span> <span class="w">braces</span></li><li>   \<span class="w">B</span><span class="s">{</span><span class="s">}</span> <span class="w">Match</span> <span class="w">wherever</span> \<span class="w">b</span><span class="s">{</span><span class="s">}</span> <span class="w">doesn&#39;t</span> <span class="w">match</span></li><li>   \<span class="w">b</span> <span class="w">Match</span> <span class="w">word</span> <span class="w">boundary</span> <span class="s">(</span><span class="w">between</span> \<span class="w">w</span> <a class="l_k" href="functions/and.html">and</a> \<span class="w">W</span><span class="s">)</span></li><li>   \<span class="w">B</span> <span class="w">Match</span> <span class="w">except</span> <span class="w">at</span> <span class="w">word</span> <span class="w">boundary</span> <span class="s">(</span><span class="w">between</span> \<span class="w">w</span> <a class="l_k" href="functions/and.html">and</a> \<span class="w">w</span> <a class="l_k" href="functions/or.html">or</a> \<span class="w">W</span> <a class="l_k" href="functions/and.html">and</a> \<span class="w">W</span><span class="s">)</span></li><li>   \<span class="w">A</span> <span class="w">Match</span> <span class="w">string</span> <span class="w">start</span> <span class="s">(</span><span class="w">regardless</span> <span class="w">of</span> /<span class="q">m)</span></li><li>   <span class="q">   \Z Match string end (before optional newline)</span></li><li>   \<span class="w">z</span> <span class="w">Match</span> <span class="w">absolute</span> <span class="w">string</span> <span class="w">end</span></li><li>   \<span class="w">G</span> <span class="w">Match</span> <span class="w">where</span> <span class="w">previous</span> <span class="q">m//g</span> <span class="w">left</span> <span class="w">off</span></li><li>   \<span class="w">K</span> <span class="w">Keep</span> <span class="w">the</span> <span class="w">stuff</span> <span class="w">left</span> <span class="w">of</span> <span class="w">the</span> \<span class="w">K</span><span class="cm">,</span> <span class="w">don&#39;t</span> <span class="w">include</span> <span class="w">it</span> <span class="w">in</span> <span class="i">$&amp;</span></li></ol></pre><a name="QUANTIFIERS"></a><h2>QUANTIFIERS</h2>
<p>Quantifiers are greedy by default and match the <b>longest</b> leftmost.</p>
<pre class="verbatim"><ol><li>   Maximal Minimal Possessive Allowed range</li><li>   ------- ------- ---------- -------------</li><li>   {n,m}   {n,m}?  {n,m}+     Must occur at least n times</li><li>                              but no more than m times</li><li>   {n,}    {n,}?   {n,}+      Must occur at least n times</li><li>   {n}     {n}?    {n}+       Must occur exactly n times</li><li>   *       *?      *+         0 or more times (same as {0,})</li><li>   +       +?      ++         1 or more times (same as {1,})</li><li>   ?       ??      ?+         0 or 1 time (same as {0,1})</li></ol></pre><p>The possessive forms (new in Perl 5.10) prevent backtracking: what gets
matched by a pattern with a possessive quantifier will not be backtracked
into, even if that causes the whole match to fail.</p>
<p>There is no quantifier <code class="inline"><span class="s">{</span><span class="cm">,</span><span class="w">n</span><span class="s">}</span></code>
. That's interpreted as a literal string.</p>
<a name="EXTENDED-CONSTRUCTS"></a><h2>EXTENDED CONSTRUCTS</h2>
<pre class="verbatim"><ol><li>   <span class="s">(</span><span class="q">?#text)          A comment</span></li><li>   <span class="q">   (?</span><span class="co">:</span>...<span class="s">)</span>           <span class="w">Groups</span> <span class="w">subexpressions</span> <span class="w">without</span> <span class="w">capturing</span> <span class="s">(</span><span class="w">cluster</span><span class="s">)</span></li><li>   <span class="s">(</span><span class="q">?pimsx-imsx:...) Enable/disable option (as per m// modifiers)</span></li><li>   <span class="q">   (?</span>=...<span class="s">)</span>           <span class="w">Zero</span>-<span class="w">width</span> <span class="w">positive</span> <span class="w">lookahead</span> <span class="i">assertion</span></li><li>   <span class="s">(</span><span class="q">?!...)           Zero-width negative lookahead assertion</span></li><li>   <span class="q">   (?</span>&lt;=...<span class="s">)</span>          <span class="w">Zero</span>-<span class="w">width</span> <span class="w">positive</span> <span class="w">lookbehind</span> <span class="i">assertion</span></li><li>   <span class="s">(</span><span class="q">?&lt;!...)          Zero-width negative lookbehind assertion</span></li><li>   <span class="q">   (?</span>&gt;...<span class="s">)</span>           <span class="w">Grab</span> <span class="w">what</span> <span class="w">we</span> <span class="w">can</span><span class="cm">,</span> <span class="w">prohibit</span> <span class="i">backtracking</span></li><li>   <span class="s">(</span><span class="q">?|...)           Branch reset</span></li><li>   <span class="q">   (?</span>&lt;<span class="w">name</span>&gt;...<span class="s">)</span>      <span class="w">Named</span> <span class="i">capture</span></li><li>   <span class="s">(</span><span class="q">?&#39;name&#39;...)      Named capture</span></li><li>   <span class="q">   (?</span><span class="w">P</span><span class="q">&lt;name&gt;</span>...<span class="s">)</span>     <span class="w">Named</span> <span class="w">capture</span> <span class="s">(</span><span class="w">python</span> <span class="w">syntax</span><span class="s">)</span></li><li>   <span class="s">(</span><span class="q">?[...])          Extended bracketed character class</span></li><li>   <span class="q">   (?</span><span class="s">{</span> <span class="w">code</span> <span class="s">}</span><span class="s">)</span>       <span class="w">Embedded</span> <span class="w">code</span><span class="cm">,</span> <a class="l_k" href="functions/return.html">return</a> <span class="w">value</span> <span class="w">becomes</span> <span class="i">$^R</span></li><li>   <span class="s">(</span><span class="q">??</span><span class="s">{</span> <span class="w">code</span> <span class="s">}</span><span class="s">)</span>      <span class="w">Dynamic</span> <span class="w">regex</span><span class="cm">,</span> <a class="l_k" href="functions/return.html">return</a> <span class="w">value</span> <span class="w">used</span> <span class="w">as</span> <span class="i">regex</span></li><li>   <span class="s">(</span><span class="q">?N)              Recurse into subpattern number N</span></li><li>   <span class="q">   (?</span>-<span class="w">N</span><span class="s">)</span><span class="cm">,</span> <span class="s">(</span><span class="q">?+N)      Recurse into Nth previous/next subpattern</span></li><li>   <span class="q">   (?</span><span class="w">R</span><span class="s">)</span><span class="cm">,</span> <span class="s">(</span><span class="q">?0)        Recurse at the beginning of the whole pattern</span></li><li>   <span class="q">   (?</span>&amp;<span class="w">name</span><span class="s">)</span>          <span class="w">Recurse</span> <span class="w">into</span> <span class="w">a</span> <span class="w">named</span> <span class="i">subpattern</span></li><li>   <span class="s">(</span><span class="q">?P&gt;name)         Recurse into a named subpattern (python syntax)</span></li><li>   <span class="q">   (?</span><span class="s">(</span><span class="w">cond</span><span class="s">)</span><span class="w">yes</span>|<a class="l_k" href="functions/no.html">no</a><span class="s">)</span></li><li>   <span class="s">(</span><span class="q">?(cond)yes)      Conditional expression, where &quot;cond&quot; can be:</span></li><li>                     <span class="q">                     (?</span>=<span class="w">pat</span><span class="s">)</span>   <span class="i">lookahead</span></li><li>                     <span class="s">(</span><span class="q">?!pat)   negative lookahead</span></li><li>                     <span class="q">                     (?</span>&lt;=<span class="w">pat</span><span class="s">)</span>  <span class="i">lookbehind</span></li><li>                     <span class="s">(</span><span class="q">?&lt;!pat)  negative lookbehind</span></li><li>                     <span class="q">                     (N)       subpattern N has matched something</span></li><li>                     <span class="q">                     (&lt;name&gt;)  named subpattern has matched something</span></li><li>                     <span class="q">                     (&#39;name&#39;)  named subpattern has matched something</span></li><li>                     <span class="q">                     (?</span><span class="s">{</span><span class="w">code</span><span class="s">}</span><span class="s">)</span> <span class="w">code</span> <span class="i">condition</span></li><li>                     <span class="s">(</span><span class="w">R</span><span class="s">)</span>       <span class="w">true</span> <a class="l_k" href="functions/if.html">if</a> <span class="i">recursing</span></li><li>                     <span class="s">(</span><span class="w">RN</span><span class="s">)</span>      <span class="w">true</span> <a class="l_k" href="functions/if.html">if</a> <span class="w">recursing</span> <span class="w">into</span> <span class="w">Nth</span> <span class="i">subpattern</span></li><li>                     <span class="s">(</span><span class="w">R</span><span class="i">&amp;name</span><span class="s">)</span>  <span class="w">true</span> <a class="l_k" href="functions/if.html">if</a> <span class="w">recursing</span> <span class="w">into</span> <span class="w">named</span> <span class="i">subpattern</span></li><li>                     <span class="s">(</span><span class="w">DEFINE</span><span class="s">)</span>  <span class="w">always</span> <span class="w">false</span><span class="cm">,</span> <a class="l_k" href="functions/no.html">no</a> <a class="l_k" href="functions/no.html">no</a>-<span class="w">pattern</span> <span class="w">allowed</span></li></ol></pre><a name="VARIABLES"></a><h2>VARIABLES</h2>
<pre class="verbatim"><ol><li>   $_    Default variable for operators to use</li><li></li><li>   $`    Everything prior to matched string</li><li>   $&amp;    Entire matched string</li><li>   $'    Everything after to matched string</li><li></li><li>   ${^PREMATCH}   Everything prior to matched string</li><li>   ${^MATCH}      Entire matched string</li><li>   ${^POSTMATCH}  Everything after to matched string</li></ol></pre><p>Note to those still using Perl 5.18 or earlier:
The use of <code class="inline"><span class="i">$`</span></code>
, <code class="inline"><span class="i">$&amp;</span></code>
 or <code class="inline"><span class="i">$&#39;</span></code>
 will slow down <b>all</b> regex use
within your program. Consult <a href="perlvar.html">perlvar</a> for <code class="inline"><span class="i">@-</span></code>

to see equivalent expressions that won't cause slow down.
See also <a href="http://search.cpan.org/perldoc/Devel::SawAmpersand">Devel::SawAmpersand</a>. Starting with Perl 5.10, you
can also use the equivalent variables <code class="inline"><span class="i">$</span>{<span class="w">^PREMATCH</span>}</code>
, <code class="inline"><span class="i">$</span>{<span class="w">^MATCH</span>}</code>

and <code class="inline"><span class="i">$</span>{<span class="w">^POSTMATCH</span>}</code>
, but for them to be defined, you have to
specify the <code class="inline">/p</code> (preserve) modifier on your regular expression.
In Perl 5.20, the use of <code class="inline"><span class="i">$`</span></code>
, <code class="inline"><span class="i">$&amp;</span></code>
 and <code class="inline"><span class="i">$&#39;</span></code>
 makes no speed difference.</p>
<pre class="verbatim"><ol><li>   <span class="i">$1</span><span class="cm">,</span> <span class="i">$2</span> ...  <span class="w">hold</span> <span class="w">the</span> <span class="w">Xth</span> <span class="w">captured</span> <span class="w">expr</span></li><li>   <span class="i">$+</span>    <span class="w">Last</span> <span class="w">parenthesized</span> <span class="w">pattern</span> <span class="w">match</span></li><li>   <span class="i">$^N</span>   <span class="w">Holds</span> <span class="w">the</span> <span class="w">most</span> <span class="w">recently</span> <span class="w">closed</span> <span class="w">capture</span></li><li>   <span class="i">$^R</span>   <span class="w">Holds</span> <span class="w">the</span> <span class="w">result</span> <span class="w">of</span> <span class="w">the</span> <a class="l_k" href="functions/last.html">last</a> <span class="s">(</span><span class="q">?{...}) expr</span></li><li>   <span class="q">   @-    Offsets of starts of groups. $-[0] holds start of whole match</span></li><li>   <span class="q">   @+    Offsets of ends of groups. $+[0] holds end of whole match</span></li><li>   <span class="q">   %+    Named capture groups</span></li><li>   <span class="q">   %-    Named capture groups, as array refs</span></li></ol></pre><p>Captured groups are numbered according to their <i>opening</i> paren.</p>
<a name="FUNCTIONS"></a><h2>FUNCTIONS</h2>
<pre class="verbatim"><ol><li>   <a class="l_k" href="functions/lc.html">lc</a>          <span class="w">Lowercase</span> <span class="w">a</span> <span class="w">string</span></li><li>   <a class="l_k" href="functions/lcfirst.html">lcfirst</a>     <span class="w">Lowercase</span> <span class="w">first</span> <span class="w">char</span> <span class="w">of</span> <span class="w">a</span> <span class="w">string</span></li><li>   <a class="l_k" href="functions/uc.html">uc</a>          <span class="w">Uppercase</span> <span class="w">a</span> <span class="w">string</span></li><li>   <a class="l_k" href="functions/ucfirst.html">ucfirst</a>     <span class="w">Titlecase</span> <span class="w">first</span> <span class="w">char</span> <span class="w">of</span> <span class="w">a</span> <span class="w">string</span></li><li>   <span class="w">fc</span>          <span class="w">Foldcase</span> <span class="w">a</span> <span class="w">string</span></li><li></li><li>   <a class="l_k" href="functions/pos.html">pos</a>         <span class="w">Return</span> <a class="l_k" href="functions/or.html">or</a> <span class="w">set</span> <span class="w">current</span> <span class="w">match</span> <span class="w">position</span></li><li>   <a class="l_k" href="functions/quotemeta.html">quotemeta</a>   <span class="w">Quote</span> <span class="w">metacharacters</span></li><li>   <a class="l_k" href="functions/reset.html">reset</a>       <span class="w">Reset</span> <span class="q">m?pattern?</span> <span class="w">status</span></li><li>   <a class="l_k" href="functions/study.html">study</a>       <span class="w">Analyze</span> <span class="w">string</span> <a class="l_k" href="functions/for.html">for</a> <span class="w">optimizing</span> <span class="w">matching</span></li><li></li><li>   <a class="l_k" href="functions/split.html">split</a>       <span class="w">Use</span> <span class="w">a</span> <span class="w">regex</span> <span class="w">to</span> <a class="l_k" href="functions/split.html">split</a> <span class="w">a</span> <span class="w">string</span> <span class="w">into</span> <span class="w">parts</span></li></ol></pre><p>The first five of these are like the escape sequences <code class="inline">\<span class="w">L</span></code>
, <code class="inline">\<span class="w">l</span></code>
,
<code class="inline">\<span class="w">U</span></code>
, <code class="inline">\<span class="w">u</span></code>
, and <code class="inline">\<span class="w">F</span></code>
.  For Titlecase, see <a href="#Titlecase">Titlecase</a>; For
Foldcase, see <a href="#Foldcase">Foldcase</a>.</p>
<a name="TERMINOLOGY"></a><h2>TERMINOLOGY</h2>
<a name="Titlecase"></a><h3>Titlecase</h3>
<p>Unicode concept which most often is equal to uppercase, but for
certain characters like the German "sharp s" there is a difference.</p>
<a name="Foldcase"></a><h3>Foldcase</h3>
<p>Unicode form that is useful when comparing strings regardless of case,
as certain characters have complex one-to-many case mappings. Primarily a
variant of lowercase.</p>
<a name="AUTHOR"></a><h1>AUTHOR</h1>
<p>Iain Truskett. Updated by the Perl 5 Porters.</p>
<p>This document may be distributed under the same terms as Perl itself.</p>
<a name="SEE-ALSO"></a><h1>SEE ALSO</h1>
<ul>
<li>
<p><a href="perlretut.html">perlretut</a> for a tutorial on regular expressions.</p>
</li>
<li>
<p><a href="perlrequick.html">perlrequick</a> for a rapid tutorial.</p>
</li>
<li>
<p><a href="perlre.html">perlre</a> for more details.</p>
</li>
<li>
<p><a href="perlvar.html">perlvar</a> for details on the variables.</p>
</li>
<li>
<p><a href="perlop.html">perlop</a> for details on the operators.</p>
</li>
<li>
<p><a href="perlfunc.html">perlfunc</a> for details on the functions.</p>
</li>
<li>
<p><a href="perlfaq6.html">perlfaq6</a> for FAQs on regular expressions.</p>
</li>
<li>
<p><a href="perlrebackslash.html">perlrebackslash</a> for a reference on backslash sequences.</p>
</li>
<li>
<p><a href="perlrecharclass.html">perlrecharclass</a> for a reference on character classes.</p>
</li>
<li>
<p>The <a href="re.html">re</a> module to alter behaviour and aid
debugging.</p>
</li>
<li>
<p><a href="perldebug.html#Debugging-Regular-Expressions">Debugging Regular Expressions in perldebug</a></p>
</li>
<li>
<p><a href="perluniintro.html">perluniintro</a>, <a href="perlunicode.html">perlunicode</a>, <a href="charnames.html">charnames</a> and <a href="perllocale.html">perllocale</a>
for details on regexes and internationalisation.</p>
</li>
<li>
<p><i>Mastering Regular Expressions</i> by Jeffrey Friedl
(<a href="http://oreilly.com/catalog/9780596528126/">http://oreilly.com/catalog/9780596528126/</a>) for a thorough grounding and
reference on the topic.</p>
</li>
</ul>
<a name="THANKS"></a><h1>THANKS</h1>
<p>David P.C. Wollmann,
Richard Soderberg,
Sean M. Burke,
Tom Christiansen,
Jim Cromie,
and
Jeffrey Goff
for useful advice.</p>




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