.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.32
.\" ========================================================================
.de Sh \" Subsection heading
.de Sp \" Vertical space (when we can't use .PP)
.de Vb \" Begin verbatim text
.de Ve \" End verbatim text
.\" Set up some character translations and predefined strings. \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote. | will give a
.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to
.\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C'
.\" expand to `' in nroff, nothing in troff, for use with C<>.
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
. tm Index:\\$1\t\\n%\t"\\$2"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear. Run. Save yourself. No user-serviceable parts.
. \" fudge factors for nroff and troff
. ds #H ((1u-(\\\\n(.fu%2u))*.13m)
. \" simple accents for nroff and troff
. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
. ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
. ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
. ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
. \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
. \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
. \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
.\" ========================================================================
.TH re 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide"
re \- Perl pragma to alter regular expression behaviour
\& ($x) = ($^X =~ /^(.*)$/s); # $x is tainted here
\& $pat = '(?{ $foo = 1 })';
\& /foo${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 $^X in these examples because it's tainted by default.)
When \f(CW\*(C`use re 'taint'\*(C'\fR is in effect, and a tainted string is the target
of a regex, the regex memories (or values returned by the m// operator
in list context) are tainted. This feature is useful when regex operations
on tainted data aren't meant to extract safe substrings, but to perform
When \f(CW\*(C`use re 'eval'\*(C'\fR is in effect, a regex is allowed to contain
\&\f(CW\*(C`(?{ ... })\*(C'\fR zero-width assertions even if regular expression contains
variable interpolation. That is normally disallowed, since it is a
potential security risk. Note that this pragma is ignored when the regular
expression is obtained from tainted data, i.e. evaluation is always
disallowed with tainted regular expressions. See \*(L"(?{ code })\*(R" in perlre.
For the purpose of this pragma, interpolation of precompiled regular
expressions (i.e., the result of \f(CW\*(C`qr//\*(C'\fR) is \fInot\fR considered variable
\&\fIis\fR allowed if \f(CW$pat\fR is a precompiled regular expression, even
if \f(CW$pat\fR contains \f(CW\*(C`(?{ ... })\*(C'\fR assertions.
When \f(CW\*(C`use re 'debug'\*(C'\fR is in effect, perl emits debugging messages when
compiling and using regular expressions. The output is the same as that
obtained by running a \f(CW\*(C`\-DDEBUGGING\*(C'\fR\-enabled perl interpreter with the
\&\fB\-Dr\fR switch. It may be quite voluminous depending on the complexity
of the match. Using \f(CW\*(C`debugcolor\*(C'\fR instead of \f(CW\*(C`debug\*(C'\fR enables a
form of output that can be used to get a colorful display on terminals
that understand termcap color sequences. Set \f(CW$ENV{PERL_RE_TC}\fR to a
comma-separated list of \f(CW\*(C`termcap\*(C'\fR properties to use for highlighting
strings on/off, pre-point part on/off.
See \*(L"Debugging regular expressions\*(R" in perldebug for additional info.
The directive \f(CW\*(C`use re 'debug'\*(C'\fR is \fInot lexically scoped\fR, as the
other directives are. It has both compile-time and run-time effects.
See \*(L"Pragmatic Modules\*(R" in perlmodlib.