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<html>
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<title>Chapter38.PL/Perl - Perl Procedural Language</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" lang="en" id="plperl">
<div class="titlepage"><div><div><h2 class="title">
<a name="plperl"></a>Chapter38.PL/Perl - Perl Procedural Language</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="plperl.html#plperl-funcs">38.1. PL/Perl Functions and Arguments</a></span></dt>
<dt><span class="sect1"><a href="plperl-database.html">38.2. Database Access from PL/Perl</a></span></dt>
<dt><span class="sect1"><a href="plperl-data.html">38.3. Data Values in PL/Perl</a></span></dt>
<dt><span class="sect1"><a href="plperl-global.html">38.4. Global Values in PL/Perl</a></span></dt>
<dt><span class="sect1"><a href="plperl-trusted.html">38.5. Trusted and Untrusted PL/Perl</a></span></dt>
<dt><span class="sect1"><a href="plperl-triggers.html">38.6. PL/Perl Triggers</a></span></dt>
<dt><span class="sect1"><a href="plperl-missing.html">38.7. Limitations and Missing Features</a></span></dt>
</dl>
</div>
<a name="id731256"></a><a name="id731265"></a><p> PL/Perl is a loadable procedural language that enables you to write
<span class="productname">PostgreSQL</span> functions in the
<a href="http://www.perl.com" target="_top">Perl programming language</a>.
</p>
<p> To install PL/Perl in a particular database, use
<code class="literal">createlang plperl <em class="replaceable"><code>dbname</code></em></code>.
</p>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Tip</h3>
<p> If a language is installed into <code class="literal">template1</code>, all subsequently
created databases will have the language installed automatically.
</p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p> Users of source packages must specially enable the build of
PL/Perl during the installation process. (Refer to <a href="installation.html#install-short" title="14.1.Short Version">Section14.1, “Short Version”</a> for more information.) Users of
binary packages might find PL/Perl in a separate subpackage.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="plperl-funcs"></a>38.1.PL/Perl Functions and Arguments</h2></div></div></div>
<p> To create a function in the PL/Perl language, use the standard
<a href="sql-createfunction.html">CREATE FUNCTION</a>
syntax:
</p>
<pre class="programlisting">CREATE FUNCTION <em class="replaceable"><code>funcname</code></em> (<em class="replaceable"><code>argument-types</code></em>) RETURNS <em class="replaceable"><code>return-type</code></em> AS $$
# PL/Perl function body
$$ LANGUAGE plperl;</pre>
<p>
The body of the function is ordinary Perl code. In fact, the PL/Perl
glue code wraps it inside a Perl subroutine. A PL/Perl function must
always return a scalar value. You can return more complex structures
(arrays, records, and sets) by returning a reference, as discussed below.
Never return a list.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p> The use of named nested subroutines is dangerous in Perl, especially if
they refer to lexical variables in the enclosing scope. Because a PL/Perl
function is wrapped in a subroutine, any named subroutine you create will
be nested. In general, it is far safer to create anonymous subroutines
which you call via a coderef. See the <code class="literal">perldiag</code>
man page for more details.
</p>
</div>
<p> The syntax of the <code class="command">CREATE FUNCTION</code> command requires
the function body to be written as a string constant. It is usually
most convenient to use dollar quoting (see <a href="sql-syntax.html#sql-syntax-dollar-quoting" title="4.1.2.2.Dollar-Quoted String Constants">Section4.1.2.2, “Dollar-Quoted String Constants”</a>) for the string constant.
If you choose to use regular single-quoted string constant syntax,
you must escape single quote marks (<code class="literal">'</code>) and backslashes
(<code class="literal">\</code>) used in the body of the function, typically by
doubling them (see <a href="sql-syntax.html#sql-syntax-strings" title="4.1.2.1.String Constants">Section4.1.2.1, “String Constants”</a>).
</p>
<p> Arguments and results are handled as in any other Perl subroutine:
arguments are passed in <code class="varname">@_</code>, and a result value
is returned with <code class="literal">return</code> or as the last expression
evaluated in the function.
</p>
<p> For example, a function returning the greater of two integer values
could be defined as:
</p>
<pre class="programlisting">CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
if ($_[0] > $_[1]) { return $_[0]; }
return $_[1];
$$ LANGUAGE plperl;</pre>
<p>
</p>
<p> If an SQL null value<a name="id731475"></a> is passed to a function,
the argument value will appear as “<span class="quote">undefined</span>” in Perl. The
above function definition will not behave very nicely with null
inputs (in fact, it will act as though they are zeroes). We could
add <code class="literal">STRICT</code> to the function definition to make
<span class="productname">PostgreSQL</span> do something more reasonable:
if a null value is passed, the function will not be called at all,
but will just return a null result automatically. Alternatively,
we could check for undefined inputs in the function body. For
example, suppose that we wanted <code class="function">perl_max</code> with
one null and one nonnull argument to return the nonnull argument,
rather than a null value:
</p>
<pre class="programlisting">CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
my ($x,$y) = @_;
if (! defined $x) {
if (! defined $y) { return undef; }
return $y;
}
if (! defined $y) { return $x; }
if ($x > $y) { return $x; }
return $y;
$$ LANGUAGE plperl;</pre>
<p>
As shown above, to return an SQL null value from a PL/Perl
function, return an undefined value. This can be done whether the
function is strict or not.
</p>
<p> Perl can return <span class="productname">PostgreSQL</span> arrays as
references to Perl arrays. Here is an example:
</p>
<pre class="programlisting">CREATE OR REPLACE function returns_array()
RETURNS text[][] AS $$
return [['a"b','c,d'],['e\\f','g']];
$$ LANGUAGE plperl;
select returns_array();</pre>
<p>
</p>
<p> Composite-type arguments are passed to the function as references
to hashes. The keys of the hash are the attribute names of the
composite type. Here is an example:
</p>
<pre class="programlisting">CREATE TABLE employee (
name text,
basesalary integer,
bonus integer
);
CREATE FUNCTION empcomp(employee) RETURNS integer AS $$
my ($emp) = @_;
return $emp->{basesalary} + $emp->{bonus};
$$ LANGUAGE plperl;
SELECT name, empcomp(employee.*) FROM employee;</pre>
<p>
</p>
<p> A PL/Perl function can return a composite-type result using the same
approach: return a reference to a hash that has the required attributes.
For example,
</p>
<pre class="programlisting">CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
return {f2 => 'hello', f1 => 1, f3 => 'world'};
$$ LANGUAGE plperl;
SELECT * FROM perl_row();</pre>
<p>
Any columns in the declared result data type that are not present in the
hash will be returned as NULLs.
</p>
<p> PL/Perl functions can also return sets of either scalar or
composite types. Usually you'll want to return rows one at a
time, both to speed up startup time and to keep from queueing up
the entire result set in memory. You can do this with
<code class="function">return_next</code> as illustrated below. Note that
after the last <code class="function">return_next</code>, you must put
either <code class="literal">return</code> or (better) <code class="literal">return
undef</code>.
</p>
<pre class="programlisting">CREATE OR REPLACE FUNCTION perl_set_int(int)
RETURNS SETOF INTEGER AS $$
foreach (0..$_[0]) {
return_next($_);
}
return undef;
$$ LANGUAGE plperl;
SELECT * FROM perl_set_int(5);
CREATE OR REPLACE FUNCTION perl_set()
RETURNS SETOF testrowperl AS $$
return_next({ f1 => 1, f2 => 'Hello', f3 => 'World' });
return_next({ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' });
return_next({ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' });
return undef;
$$ LANGUAGE plperl;</pre>
<p>
For small result sets, you can return a reference to an array that
contains either scalars, references to arrays, or references to
hashes for simple types, array types, and composite types,
respectively. Here are some simple examples of returning the entire
result set as an array reference:
</p>
<pre class="programlisting">CREATE OR REPLACE FUNCTION perl_set_int(int) RETURNS SETOF INTEGER AS $$
return [0..$_[0]];
$$ LANGUAGE plperl;
SELECT * FROM perl_set_int(5);
CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testrowperl AS $$
return [
{ f1 => 1, f2 => 'Hello', f3 => 'World' },
{ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
{ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
];
$$ LANGUAGE plperl;
SELECT * FROM perl_set();</pre>
<p>
</p>
<p> <span class="application">PL/Perl</span> does not currently have full support for
domain types: it treats a domain the same as the underlying scalar
type. This means that constraints associated with the domain will
not be enforced. This is not an issue for function arguments, but
it is a hazard if you declare a <span class="application">PL/Perl</span> function
as returning a domain type.
</p>
<p> If you wish to use the <code class="literal">strict</code> pragma with your code,
the easiest way to do so is to <code class="command">SET</code>
<code class="literal">plperl.use_strict</code> to true. This parameter affects
subsequent compilations of <span class="application">PL/Perl</span> functions, but not
functions already compiled in the current session. To set the
parameter before <span class="application">PL/Perl</span> has been loaded, it is
necessary to have added “<span class="quote"><code class="literal">plperl</code></span>” to the <a href="runtime-config-custom.html#guc-custom-variable-classes">custom_variable_classes</a> list in
<code class="filename">postgresql.conf</code>.
</p>
<p> Another way to use the <code class="literal">strict</code> pragma is to put
</p>
<pre class="programlisting">use strict;</pre>
<p>
in the function body. But this only works in <span class="application">PL/PerlU</span>
functions, since <code class="literal">use</code> is not a trusted operation. In
<span class="application">PL/Perl</span> functions you can instead do
</p>
<pre class="programlisting">BEGIN { strict->import(); }</pre>
<p>
</p>
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