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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>45.4. Global Values in PL/Perl</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 Vsnapshot" /><link rel="prev" href="plperl-builtins.html" title="45.3. Built-in Functions" /><link rel="next" href="plperl-trusted.html" title="45.5. Trusted and Untrusted PL/Perl" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">45.4. Global Values in PL/Perl</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl-builtins.html" title="45.3. Built-in Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 45. PL/Perl — Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plperl-trusted.html" title="45.5. Trusted and Untrusted PL/Perl">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLPERL-GLOBAL"><div class="titlepage"><div><div><h2 class="title" style="clear: both">45.4. Global Values in PL/Perl <a href="#PLPERL-GLOBAL" class="id_link">#</a></h2></div></div></div><p>
You can use the global hash <code class="varname">%_SHARED</code> to store
data, including code references, between function calls for the
lifetime of the current session.
</p><p>
Here is a simple example for shared data:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
if ($_SHARED{$_[0]} = $_[1]) {
return 'ok';
} else {
return "cannot set shared variable $_[0] to $_[1]";
}
$$ LANGUAGE plperl;
CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
return $_SHARED{$_[0]};
$$ LANGUAGE plperl;
SELECT set_var('sample', 'Hello, PL/Perl! How''s tricks?');
SELECT get_var('sample');
</pre><p>
</p><p>
Here is a slightly more complicated example using a code reference:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
$_SHARED{myquote} = sub {
my $arg = shift;
$arg =~ s/(['\\])/\\$1/g;
return "'$arg'";
};
$$ LANGUAGE plperl;
SELECT myfuncs(); /* initializes the function */
/* Set up a function that uses the quote function */
CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
my $text_to_quote = shift;
my $qfunc = $_SHARED{myquote};
return &$qfunc($text_to_quote);
$$ LANGUAGE plperl;
</pre><p>
(You could have replaced the above with the one-liner
<code class="literal">return $_SHARED{myquote}->($_[0]);</code>
at the expense of readability.)
</p><p>
For security reasons, PL/Perl executes functions called by any one SQL role
in a separate Perl interpreter for that role. This prevents accidental or
malicious interference by one user with the behavior of another user's
PL/Perl functions. Each such interpreter has its own value of the
<code class="varname">%_SHARED</code> variable and other global state. Thus, two
PL/Perl functions will share the same value of <code class="varname">%_SHARED</code>
if and only if they are executed by the same SQL role. In an application
wherein a single session executes code under multiple SQL roles (via
<code class="literal">SECURITY DEFINER</code> functions, use of <code class="command">SET ROLE</code>, etc.)
you may need to take explicit steps to ensure that PL/Perl functions can
share data via <code class="varname">%_SHARED</code>. To do that, make sure that
functions that should communicate are owned by the same user, and mark
them <code class="literal">SECURITY DEFINER</code>. You must of course take care that
such functions can't be used to do anything unintended.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl-builtins.html" title="45.3. Built-in Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plperl-trusted.html" title="45.5. Trusted and Untrusted PL/Perl">Next</a></td></tr><tr><td width="40%" align="left" valign="top">45.3. Built-in Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 45.5. Trusted and Untrusted PL/Perl</td></tr></table></div></body></html>