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re(3perl) | Perl Programmers Reference Guide | re(3perl) |
NAME¶
re - Perl pragma to alter regular expression behaviourSYNOPSIS¶
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 '/ix'; "FOO" =~ / foo /; # /ix implied no re '/x'; "FOO" =~ /foo/; # just /i implied use re 'debug'; # output debugging info during /^(.*)$/s; # compile and run time use re 'debugcolor'; # same as 'debug', but with colored output ... use re qw(Debug All); # Finer tuned debugging options. use re qw(Debug More); no re qw(Debug ALL); # Turn of all re debugging in this scope use re qw(is_regexp regexp_pattern); # import utility functions my ($pat,$mods)=regexp_pattern(qr/foo/i); if (is_regexp($obj)) { print "Got regexp: ", scalar regexp_pattern($obj); # just as perl would stringify it } # but no hassle with blessed re's.(We use $^X in these examples because it's tainted by default.)
DESCRIPTION¶
'taint' mode¶
When "use re 'taint'" is in effect, and a tainted string is the target of a regexp, the regexp memories (or values returned by the m// operator in list context) are tainted. This feature is useful when regexp operations on tainted data aren't meant to extract safe substrings, but to perform other transformations.'eval' mode¶
When "use re 'eval'" is in effect, a regexp is allowed to contain "(?{ ... })" zero-width assertions and "(??{ ... })" postponed subexpressions, even if the regular expression contains variable interpolation. That is normally disallowed, since it is a potential security risk. Note that this pragma is ignored when the regular expression is obtained from tainted data, i.e. evaluation is always disallowed with tainted regular expressions. See "(?{ code })" in perlre and "(??{ code })" in perlre. For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result of "qr//") is not considered variable interpolation. Thus:/foo${pat}bar/is allowed if $pat is a precompiled regular expression, even if $pat contains "(?{ ... })" assertions or "(??{ ... })" subexpressions.
'/flags' mode¶
When "use re '/flags'" is specified, the given flags are automatically added to every regular expression till the end of the lexical scope. "no re '/flags'" will turn off the effect of "use re '/flags'" for the given flags. For example, if you want all your regular expressions to have /msx on by default, simply putuse re '/msx';at the top of your code. The character set /adul flags cancel each other out. So, in this example,
use re "/u"; "ss" =~ /\xdf/; use re "/d"; "ss" =~ /\xdf/;the second "use re" does an implicit "no re '/u'". Turning on one of the character set flags with "use re" takes precedence over the "locale" pragma and the 'unicode_strings' "feature", for regular expressions. Turning off one of these flags when it is active reverts to the behaviour specified by whatever other pragmata are in scope. For example:
use feature "unicode_strings"; no re "/u"; # does nothing use re "/l"; no re "/l"; # reverts to unicode_strings behaviour
'debug' mode¶
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. As of 5.9.5 the directive "use re 'debug'" and its equivalents are lexically scoped, as the other directives are. However they have both compile-time and run-time effects. See "Pragmatic Modules" in perlmodlib.'Debug' mode¶
Similarly "use re 'Debug'" produces debugging output, the difference being that it allows the fine tuning of what debugging output will be emitted. Options are divided into three groups, those related to compilation, those related to execution and those related to special purposes. The options are as follows:- Compile related options
- COMPILE
- Turns on all compile related debug options.
- PARSE
- Turns on debug output related to the process of parsing the pattern.
- OPTIMISE
- Enables output related to the optimisation phase of compilation.
- TRIEC
- Detailed info about trie compilation.
- DUMP
- Dump the final program out after it is compiled and optimised.
- Execute related options
- EXECUTE
- Turns on all execute related debug options.
- MATCH
- Turns on debugging of the main matching loop.
- TRIEE
- Extra debugging of how tries execute.
- INTUIT
- Enable debugging of start point optimisations.
- Extra debugging options
- EXTRA
- Turns on all "extra" debugging options.
- BUFFERS
- Enable debugging the capture group storage during match. Warning, this can potentially produce extremely large output.
- TRIEM
- Enable enhanced TRIE debugging. Enhances both TRIEE and TRIEC.
- STATE
- Enable debugging of states in the engine.
- STACK
- Enable debugging of the recursion stack in the engine. Enabling or disabling this option automatically does the same for debugging states as well. This output from this can be quite large.
- OPTIMISEM
- Enable enhanced optimisation debugging and start point optimisations. Probably not useful except when debugging the regexp engine itself.
- OFFSETS
- Dump offset information. This can be used to see how regops
correlate to the pattern. Output format is
NODENUM:POSITION[LENGTH]
- OFFSETSDBG
- Enable debugging of offsets information. This emits copious
amounts of trace information and doesn't mesh well with other debug
options.
- Other useful flags
- These are useful shortcuts to save on the typing.
- ALL
- Enable all options at once except OFFSETS, OFFSETSDBG and BUFFERS
- All
- Enable DUMP and all execute options. Equivalent to:
use re 'debug';
- MORE
- More
- Enable TRIEM and all execute compile and execute options.
Exportable Functions¶
As of perl 5.9.5 're' debug contains a number of utility functions that may be optionally exported into the caller's namespace. They are listed below.- is_regexp($ref)
- Returns true if the argument is a compiled regular
expression as returned by "qr//", false if it is not.
- regexp_pattern($ref)
- If the argument is a compiled regular expression as
returned by "qr//", then this function returns the pattern.
my ($pat, $mods) = regexp_pattern($ref);
if (regexp_pattern($ref) eq '(?^i:foo)')
- regmust($ref)
- If the argument is a compiled regular expression as
returned by "qr//", then this function returns what the
optimiser considers to be the longest anchored fixed string and longest
floating fixed string in the pattern.
my $qr = qr/here .* there/x; my ($anchored, $floating) = regmust($qr); print "anchored:'$anchored'\nfloating:'$floating'\n";
anchored:'here' floating:'there'
- regname($name,$all)
- Returns the contents of a named buffer of the last successful match. If $all is true, then returns an array ref containing one entry per buffer, otherwise returns the first defined buffer.
- regnames($all)
- Returns a list of all of the named buffers defined in the last successful match. If $all is true, then it returns all names defined, if not it returns only names which were involved in the match.
- regnames_count()
- Returns the number of distinct names defined in the pattern
used for the last successful match.
SEE ALSO¶
"Pragmatic Modules" in perlmodlib.2011-09-19 | perl v5.14.2 |