re(3)

NAME
     re - Perl pragma to alter regular expression behaviour

SYNOPSIS
         ($x) = ($^X =~ /^(.*)$/s);     # $x is not tainted here

         use re "taint";
         ($x) = ($^X =~ /^(.*)$/s);     # $x _is_ tainted here

     (We use $^X in these examples because it's tainted by default.)

DESCRIPTION
     When use re 'taint' 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.

     See the section on Pragmatic Modules in the perlmodlib manpage.