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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>44.1. PL/Perl Functions and Arguments</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language" /><link rel="next" href="plperl-data.html" title="44.2. Data Values in PL/Perl" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.1. PL/Perl Functions and Arguments</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Perl - Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plperl-data.html" title="44.2. Data Values in PL/Perl">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPERL-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.1. PL/Perl Functions and Arguments</h2></div></div></div><p>
   To create a function in the PL/Perl language, use the standard
   <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></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 is
   called in a scalar context, so it can't return a list.  You can return
   non-scalar values (arrays, records, and sets) by returning a reference,
   as discussed below.
  </p><p>
   In a PL/Perl procedure, any return value from the Perl code is ignored.
  </p><p>
   PL/Perl also supports anonymous code blocks called with the
   <a class="xref" href="sql-do.html" title="DO"><span class="refentrytitle">DO</span></a> statement:

</p><pre class="programlisting">
DO $$
    # PL/Perl code
$$ LANGUAGE plperl;
</pre><p>

   An anonymous code block receives no arguments, and whatever value it
   might return is discarded.  Otherwise it behaves just like a function.
  </p><div class="note"><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 place inside
    one will be nested. In general, it is far safer to create anonymous
    subroutines which you call via a coderef. For more information, see the
    entries for <code class="literal">Variable "%s" will not stay shared</code> and
    <code class="literal">Variable "%s" is not available</code> in the
    <span class="citerefentry"><span class="refentrytitle">perldiag</span></span> man page, or
    search the Internet for <span class="quote">“<span class="quote">perl nested named subroutine</span>”</span>.
   </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 class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING" title="4.1.2.4. Dollar-Quoted String Constants">Section 4.1.2.4</a>) for the string constant.
   If you choose to use escape string syntax <code class="literal">E''</code>,
   you must double any single quote marks (<code class="literal">'</code>) and backslashes
   (<code class="literal">\</code>) used in the body of the function
   (see <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" title="4.1.2.1. String Constants">Section 4.1.2.1</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 $$
    if ($_[0] &gt; $_[1]) { return $_[0]; }
    return $_[1];
$$ LANGUAGE plperl;
</pre><p>
  </p><div class="note"><h3 class="title">Note</h3><p>
      Arguments will be converted from the database's encoding to UTF-8
      for use inside PL/Perl, and then converted from UTF-8 back to the
      database encoding upon return.
    </p></div><p>
   If an SQL null value<a id="id-1.8.10.9.10.1" class="indexterm"></a> is passed to a function,
   the argument value will appear as <span class="quote">“<span class="quote">undefined</span>”</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 $$
    my ($x, $y) = @_;
    if (not defined $x) {
        return undef if not defined $y;
        return $y;
    }
    return $x if not defined $y;
    return $x if $x &gt; $y;
    return $y;
$$ 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>
   Anything in a function argument that is not a reference is
   a string, which is in the standard <span class="productname">PostgreSQL</span>
   external text representation for the relevant data type. In the case of
   ordinary numeric or text types, Perl will just do the right thing and
   the programmer will normally not have to worry about it. However, in
   other cases the argument will need to be converted into a form that is
   more usable in Perl. For example, the <code class="function">decode_bytea</code>
   function can be used to convert an argument of
   type <code class="type">bytea</code> into unescaped binary.
  </p><p>
   Similarly, values passed back to <span class="productname">PostgreSQL</span>
   must be in the external text representation format. For example, the
   <code class="function">encode_bytea</code> function can be used to
   escape binary data for a return value of type <code class="type">bytea</code>.
  </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>
   Perl passes <span class="productname">PostgreSQL</span> arrays as a blessed
   <code class="type">PostgreSQL::InServer::ARRAY</code> object. This object may be treated as an array
   reference or a string, allowing for backward compatibility with Perl
   code written for <span class="productname">PostgreSQL</span> versions below 9.1 to
   run.  For example:

</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION concat_array_elements(text[]) RETURNS TEXT AS $$
    my $arg = shift;
    my $result = "";
    return undef if (!defined $arg);

    # as an array reference
    for (@$arg) {
        $result .= $_;
    }

    # also works as a string
    $result .= $arg;

    return $result;
$$ LANGUAGE plperl;

SELECT concat_array_elements(ARRAY['PL','/','Perl']);
</pre><p>

  </p><div class="note"><h3 class="title">Note</h3><p>
    Multidimensional arrays are represented as references to
    lower-dimensional arrays of references in a way common to every Perl
    programmer.
   </p></div><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 $$
    my ($emp) = @_;
    return $emp-&gt;{basesalary} + $emp-&gt;{bonus};
$$ 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 $$
    return {f2 =&gt; 'hello', f1 =&gt; 1, f3 =&gt; 'world'};
$$ 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 null values.
  </p><p>
   Similarly, output arguments of procedures can be returned as a hash
   reference:

</p><pre class="programlisting">
CREATE PROCEDURE perl_triple(INOUT a integer, INOUT b integer) AS $$
    my ($a, $b) = @_;
    return {a =&gt; $a * 3, b =&gt; $b * 3};
$$ LANGUAGE plperl;

CALL perl_triple(5, 10);
</pre><p>
  </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 queuing 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 $$
    return_next({ f1 =&gt; 1, f2 =&gt; 'Hello', f3 =&gt; 'World' });
    return_next({ f1 =&gt; 2, f2 =&gt; 'Hello', f3 =&gt; 'PostgreSQL' });
    return_next({ f1 =&gt; 3, f2 =&gt; 'Hello', f3 =&gt; 'PL/Perl' });
    return undef;
$$ 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 $$
    return [
        { f1 =&gt; 1, f2 =&gt; 'Hello', f3 =&gt; 'World' },
        { f1 =&gt; 2, f2 =&gt; 'Hello', f3 =&gt; 'PostgreSQL' },
        { f1 =&gt; 3, f2 =&gt; 'Hello', f3 =&gt; 'PL/Perl' }
    ];
$$ LANGUAGE plperl;

SELECT * FROM perl_set();
</pre><p>
  </p><p>
   If you wish to use the <code class="literal">strict</code> pragma with your code you
   have a few options. For temporary global use you can <code class="command">SET</code>
   <code class="literal">plperl.use_strict</code> to true.
   This will affect subsequent compilations of <span class="application">PL/Perl</span>
   functions, but not functions already compiled in the current session.
   For permanent global use you can set <code class="literal">plperl.use_strict</code>
   to true in the <code class="filename">postgresql.conf</code> file.
  </p><p>
   For permanent use in specific functions you can simply put:
</p><pre class="programlisting">
use strict;
</pre><p>
   at the top of the function body.
  </p><p>
  The <code class="literal">feature</code> pragma is also available to <code class="function">use</code> if your Perl is version 5.10.0 or higher.
  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plperl-data.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 44. PL/Perl - Perl Procedural Language </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 44.2. Data Values in PL/Perl</td></tr></table></div></body></html>