 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 targetof a regexp, the regexp memories (or values returned by the m// operatorin list context) are tainted. This feature is useful when regexp operationson tainted data aren't meant to extract safe substrings, but to performother transformations.

'eval' mode

When use re 'eval' is in effect, a regexp is allowed to contain(?{ ... }) zero-width assertions and (??{ ... }) postponedsubexpressions, even if the regular expression containsvariable interpolation. That is normally disallowed, since it is apotential security risk. Note that this pragma is ignored when the regularexpression is obtained from tainted data, i.e. evaluation is alwaysdisallowed with tainted regular expressions. See (?{ code }) in perlre and (??{ code }) in perlre.

For the purpose of this pragma, interpolation of precompiled regularexpressions (i.e., the result of qr//) is not considered variableinterpolation. Thus:

 /foo${pat}bar/

is allowed if $pat is a precompiled regular expression, evenif $pat contains (?{ ... }) assertions or (??{ ... }) subexpressions.

'/flags' mode

When use re '/flags' is specified, the given flags are automaticallyadded to every regular expression till the end of the lexical scope.

no re '/flags' will turn off the effect of use re '/flags' for thegiven flags.

For example, if you want all your regular expressions to have /msx on bydefault, simply put

 use 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 thelocale pragma and the 'unicode_strings' feature, for regularexpressions. Turning off one of these flags when it is active reverts tothe behaviour specified by whatever other pragmata are in scope. Forexample:

 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 whencompiling and using regular expressions. The output is the same as thatobtained by running a -DDEBUGGING-enabled perl interpreter with the-Dr switch. It may be quite voluminous depending on the complexityof the match. Using debugcolor instead of debug enables aform of output that can be used to get a colorful display on terminalsthat understand termcap color sequences. Set $ENV{PERL_RE_TC} to acomma-separated list of termcap properties to use for highlightingstrings 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 arelexically 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 differencebeing that it allows the fine tuning of what debugging output will beemitted. Options are divided into three groups, those related tocompilation, those related to execution and those related to specialpurposes. 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 TRIEEand TRIEC.
- STATE
  Enable debugging of states in the engine.
- STACK
  Enable debugging of the recursion stack in the engine. Enablingor disabling this option automatically does the same for debuggingstates 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 correlateto the pattern. Output format is
```
   NODENUM:POSITION[LENGTH]
 
```
  Where 1 is the position of the first char in the string. Note that positioncan be 0, or larger than the actual length of the pattern, likewise lengthcan be zero.
- OFFSETSDBG
  Enable debugging of offsets information. This emits copiousamounts of trace information and doesn't mesh well with otherdebug options.
  Almost definitely only useful to people hackingon the offsets part of the debug engine.
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.

As of 5.9.5 the directive use re 'debug' and its equivalents arelexically scoped, as the other directives are. However they have bothcompile-time and run-time effects.

Exportable Functions

As of perl 5.9.5 're' debug contains a number of utility functions thatmay be optionally exported into the caller's namespace. They are listedbelow.

is_regexp($ref)
Returns true if the argument is a compiled regular expression as returnedby qr//, false if it is not.
This function will not be confused by overloading or blessing. Ininternals terms, this extracts the regexp pointer out of thePERL_MAGIC_qr structure so it cannot be fooled.
regexp_pattern($ref)
If the argument is a compiled regular expression as returned by qr//,then this function returns the pattern.
In list context it returns a two element list, the first elementcontaining the pattern and the second containing the modifiers used whenthe pattern was compiled.
```
  my ($pat, $mods) = regexp_pattern($ref);
 
```
In scalar context it returns the same as perl would when stringifying a rawqr// with the same pattern inside. If the argument is not a compiledreference then this routine returns false but defined in scalar context,and the empty list in list context. Thus the following
```
 if (regexp_pattern($ref) eq '(?^i:foo)')
 
```
will be warning free regardless of what $ref actually is.
Like is_regexp this function will not be confused by overloadingor blessing of the object.
regmust($ref)
If the argument is a compiled regular expression as returned by qr//,then this function returns what the optimiser considers to be the longestanchored fixed string and longest floating fixed string in the pattern.
A fixed string is defined as being a substring that must appear for thepattern to match. An anchored fixed string is a fixed string that mustappear at a particular offset from the beginning of the match. A floatingfixed string is defined as a fixed string that can appear at any point ina range of positions relative to the start of the match. For example,
```
 my $qr = qr/here .* there/x;
  my ($anchored, $floating) = regmust($qr);
  print "anchored:'$anchored'\nfloating:'$floating'\n";
 
```
results in
```
 anchored:'here'
  floating:'there'
 
```
Because the here is before the .* in the pattern, its positioncan be determined exactly. That's not true, however, for the there;it could appear at any point after where the anchored string appeared.Perl uses both for its optimisations, prefering the longer, or, if they areequal, the floating.
NOTE: This may not necessarily be the definitive longest anchored andfloating string. This will be what the optimiser of the Perl that youare using thinks is the longest. If you believe that the result is wrongplease report it via the perlbug utility.
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 successfulmatch. If $all is true, then it returns all names defined, if not it returnsonly names which were involved in the match.
regnames_count()
Returns the number of distinct names defined in the pattern usedfor the last successful match.
Note: this result is always the actual number of distinctnamed buffers defined, it may not actually match that which isreturned by regnames() and related routines when those routineshave not been called with the $all parameter set.

Perl pragma to alter regular expression behaviour

Daftar Isi

NAME

SYNOPSIS