($x) = ($^X =~ /^(.*)$/s); # $x is tainted here</PRE>
<PRE>
$pat = '(?{ $foo = 1 })';
use re 'eval';
/foo${pat}bar/; # won't fail (when not under -T switch)</PRE>
<PRE>
{
no re 'taint'; # the default
($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here</PRE>
<PRE>
no re 'eval'; # the default
/foo${pat}bar/; # disallowed (with or without -T switch)
}</PRE>
<PRE>
use re 'debug'; # NOT lexically scoped (as others are)
/^(.*)$/s; # output debugging info during
# compile and run time</PRE>
<PRE>
use re 'debugcolor'; # same as 'debug', but with colored output
...</PRE>
<P>(We use $^X in these examples because it's tainted by default.)</P>
<P>
<HR>
<H1><A NAME="description">DESCRIPTION</A></H1>
<P>When <CODE>use re 'taint'</CODE> is in effect, and a tainted string is the target
of a regex, the regex memories (or values returned by the m// operator
in list context) are tainted. This feature is useful when regex operations
on tainted data aren't meant to extract safe substrings, but to perform
other transformations.</P>
<P>When <CODE>use re 'eval'</CODE> is in effect, a regex is allowed to contain
<CODE>(?{ ... })</CODE> zero-width assertions even if regular expression contains
variable interpolation. That is normally disallowed, since it is a
potential security risk. Note that this pragma is ignored when the regular
expression is obtained from tainted data, i.e. evaluation is always
disallowed with tainted regular expresssions. See <A HREF="../lib/Pod/perlre.html#({ code })">(?{ code }) in the perlre manpage</A>.</P>
<P>For the purpose of this pragma, interpolation of precompiled regular
expressions (i.e., the result of <CODE>qr//</CODE>) is <EM>not</EM> considered variable
interpolation. Thus:</P>
<PRE>
/foo${pat}bar/</PRE>
<P><EM>is</EM> allowed if $pat is a precompiled regular expression, even
if $pat contains <CODE>(?{ ... })</CODE> assertions.</P>
<P>When <CODE>use re 'debug'</CODE> is in effect, perl emits debugging messages when
compiling and using regular expressions. The output is the same as that
obtained by running a <CODE>-DDEBUGGING</CODE>-enabled perl interpreter with the
<STRONG>-Dr</STRONG> switch. It may be quite voluminous depending on the complexity
of the match. Using <CODE>debugcolor</CODE> instead of <CODE>debug</CODE> enables a
form of output that can be used to get a colorful display on terminals
that understand termcap color sequences. Set <CODE>$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="../lib/Pod/perldebug.html#debugging regular expressions">Debugging regular expressions in the perldebug manpage</A> for additional info.</P>
<P>The directive <CODE>use re 'debug'</CODE> is <EM>not lexically scoped</EM>, as the
other directives are. It has both compile-time and run-time effects.</P>
<P>See <A HREF="../lib/Pod/perlmodlib.html#pragmatic modules">Pragmatic Modules in the perlmodlib manpage</A>.</P>
