re - Perl pragma to alter regular expression behaviour

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This feature is useful when regex operations on tainted data aren't meant to extract safe substrings, but to perform other transformations.</p> <p>When <code>use re 'eval'</code> is in effect, a regex is allowed to contain <code>(?{ ... })</code> zero-width assertions even if the regex contains variable interpolation. This is normally disallowed, since it is a potential security risk. Note that this pragma is ignored when the regular expression is obtained from tainted data, i.e. evaluation is always disallowed with tainted regular expressions. See <a href="/5.005_03/perlre#(%3F%7B-code-%7D)">"(?{ code })" in perlre</a>.</p> <p>For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result of <code>qr//</code>) is <i>not</i> considered variable interpolation. Thus:</p> <pre><code class="plaintext">/foo${pat}bar/</code></pre> <p><i>is</i> allowed if $pat is a precompiled regular expression, even if $pat contains <code>(?{ ... })</code> assertions.</p> <p>When <code>use re 'debug'</code> is in effect, perl emits debugging messages when compiling and using regular expressions. The output is the same as that obtained by running a <code>-DDEBUGGING</code>-enabled perl interpreter with the <b>-Dr</b> switch. It may be quite voluminous depending on the complexity of the match. Using <code>debugcolor</code> instead of <code>debug</code> enables a form of output that can be used to get a colorful display on terminals that understand termcap color sequences. Set <code>$ENV{PERL_RE_TC}</code> to a comma-separated list of <code>termcap</code> properties to use for highlighting strings on/off, pre-point part on/off. See <a href="/5.005_03/perldebug#Debugging-regular-expressions">"Debugging regular expressions" in perldebug</a> for additional info.</p> <p>The directive <code>use re 'debug'</code> is <i>not lexically scoped</i>, as the other directives are. It has both compile-time and run-time effects.</p> <p>See <a href="/5.005_03/perlmodlib#Pragmatic-Modules">"Pragmatic Modules" in perlmodlib</a>.</p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. 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