re(3) Perl Programmers Reference Guide re(3)NAMEre - Perl pragma to alter regular expression behaviour
SYNOPSIS
use re 'taint';
($x) = ($^X =~ /^(.*)$/s); # $x is tainted here
$pat = '(?{ $foo = 1 })';
use re 'eval';
/foo${pat}bar/; # won't fail (when not under -T switch)
{
no re 'taint'; # the default
($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here
no re 'eval'; # the default
/foo${pat}bar/; # disallowed (with or without -T switch)
}
use re 'debug'; # NOT lexically scoped (as others are)
/^(.*)$/s; # output debugging info during
# compile and run time
use re 'debugcolor'; # same as 'debug', but with colored output
...
(We use $^X in these examples because it's tainted by default.)
DESCRIPTION
When "use re 'taint'" is in effect, and a tainted string is the target
of a regex, the regex memories (or values returned by the m// operator
in list context) are tainted. This feature is useful when regex opera-
tions on tainted data aren't meant to extract safe substrings, but to
perform other transformations.
When "use re 'eval'" is in effect, a regex is allowed to contain "(?{
... })" zero-width assertions even if regular expression contains vari-
able interpolation. That is normally disallowed, since it is a poten-
tial security risk. Note that this pragma is ignored when the regular
expression is obtained from tainted data, i.e. evaluation is always
disallowed with tainted regular expressions. See "(?{ code })" in
perlre.
For the purpose of this pragma, interpolation of precompiled regular
expressions (i.e., the result of "qr//") is not considered variable
interpolation. Thus:
/foo${pat}bar/
is allowed if $pat is a precompiled regular expression, even if $pat
contains "(?{ ... })" assertions.
When "use re 'debug'" is in effect, perl emits debugging messages when
compiling and using regular expressions. The output is the same as
that obtained by running a "-DDEBUGGING"-enabled perl interpreter with
the -Dr switch. It may be quite voluminous depending on the complexity
of the match. Using "debugcolor" instead of "debug" enables a form of
output that can be used to get a colorful display on terminals that
understand termcap color sequences. Set $ENV{PERL_RE_TC} to a comma-
separated list of "termcap" properties to use for highlighting strings
on/off, pre-point part on/off. See "Debugging regular expressions" in
perldebug for additional info.
The directive "use re 'debug'" is not lexically scoped, as the other
directives are. It has both compile-time and run-time effects.
See "Pragmatic Modules" in perlmodlib.
perl v5.8.8 2006-06-14 re(3)
