new¶

 my $re = PPIx::Regexp->new('/foo/');

This method instantiates a "PPIx::Regexp" object from a string, a PPI::Token::QuoteLike::Regexp, a PPI::Token::Regexp::Match, or a PPI::Token::Regexp::Substitute. Honestly, any PPI::Element will work, but only the three Regexp classes mentioned previously are likely to do anything useful.

Whatever form the argument takes, it is assumed to consist entirely of a valid match, substitution, or "qr<>" string.

Optionally you can pass one or more name/value pairs after the regular expression. The possible options are:

default_modifiers array_reference

This option specifies a reference to an array of default modifiers to apply to the regular expression being parsed. Each modifier is specified as a string. Any actual modifiers found supersede the defaults.

When applying the defaults, '?' and '/' are completely ignored, and '^' is ignored unless it occurs at the beginning of the modifier. The first dash ('-') causes subsequent modifiers to be negated.

So, for example, if you wish to produce a "PPIx::Regexp" object representing the regular expression in

 use re '/smx';
 {
    no re '/x';
    m/ foo /;
 }
    

you would (after some help from PPI in finding the relevant statements), do something like

 my $re = PPIx::Regexp->new( 'm/ foo /',
     default_modifiers => [ '/smx', '-/x' ] );
    

encoding name

This option specifies the encoding of the regular expression. This is passed to the tokenizer, which will "decode" the regular expression string before it tokenizes it. For example:

 my $re = PPIx::Regexp->new( '/foo/',
     encoding => 'iso-8859-1',
 );
    

index_locations Boolean

This Boolean option specifies whether the locations of the elements in the regular expression should be indexed.

If unspecified or specified as "undef" a default value is used. This default is true if the argument is a PPI::Element or the "location" option was specified. Otherwise the default is false.

location array_reference

This option specifies the location of the new object in the document from which it was created. It is a reference to a five-element array compatible with that returned by the "location()" method of PPI::Element.

If not specified, the location of the original string is used if it was specified as a PPI::Element.

If no location can be determined, the various "location()" methods will return "undef".

postderef Boolean

THIS ARGUMENT IS DEPRECATED. See DEPRECATION NOTICE above for the details.

This option is passed on to the tokenizer, where it specifies whether postfix dereferences are recognized in interpolations and code. This experimental feature was introduced in Perl 5.19.5.

As of version 0.074_01, the default is true. Through release 0.074, the default was the value of $PPIx::Regexp::Tokenizer::DEFAULT_POSTDEREF, which was true. When originally introduced this was false, but was documented as becoming true when and if postfix dereferencing became mainstream. The intent to mainstream was announced with Perl 5.23.1, and became official (so to speak) with Perl 5.24.0, so the default became true with PPIx::Regexp 0.049_01.

Note that if PPI starts unconditionally recognizing postfix dereferences, this argument will immediately become ignored, and will be put through a deprecation cycle and removed.

strict Boolean

This option is passed on to the tokenizer and lexer, where it specifies whether the parse should assume "use re 'strict'" is in effect.

The 'strict' pragma was introduced in Perl 5.22, and its documentation says that it is experimental, and that there is no commitment to backward compatibility. The same applies to the parse produced when this option is asserted. Also, the usual caveat applies: if "use re 'strict'" ends up being retracted, this option and all related functionality will be also.

Given the nature of "use re 'strict'", you should expect that if you assert this option, regular expressions that previously parsed without error might no longer do so. If an element ends up being declared an error because this option is set, its "perl_version_introduced()" will be the Perl version at which "use re 'strict'" started rejecting these elements.

The default is false.

trace number

If greater than zero, this option causes trace output from the parse. The author reserves the right to change or eliminate this without notice.

Passing optional input other than the above is not an error, but neither is it supported.

new_from_cache¶

This static method wraps "new" in a caching mechanism. Only one object will be generated for a given PPI::Element, no matter how many times this method is called. Calls after the first for a given PPI::Element simply return the same "PPIx::Regexp" object.

When the "PPIx::Regexp" object is returned from cache, the values of the optional arguments are ignored.

Calls to this method with the regular expression in a string rather than a PPI::Element will not be cached.

Caveat: This method is provided for code like Perl::Critic which might instantiate the same object multiple times. The cache will persist until "flush_cache" is called.

flush_cache¶

 $re->flush_cache();            # Remove $re from cache
 PPIx::Regexp->flush_cache();   # Empty the cache

This method flushes the cache used by "new_from_cache". If called as a static method with no arguments, the entire cache is emptied. Otherwise any objects specified are removed from the cache.

capture_names¶

 foreach my $name ( $re->capture_names() ) {
     print "Capture name '$name'\n";
 }

This convenience method returns the capture names found in the regular expression.

This method is equivalent to

 $self->regular_expression()->capture_names();

except that if "$self->regular_expression()" returns "undef" (meaning that something went terribly wrong with the parse) this method will simply return.

delimiters¶

 print join("\t", PPIx::Regexp->new('s/foo/bar/')->delimiters());
 # prints '//      //'

When called in list context, this method returns either one or two strings, depending on whether the parsed expression has a replacement string. In the case of non-bracketed substitutions, the start delimiter of the replacement string is considered to be the same as its finish delimiter, as illustrated by the above example.

When called in scalar context, you get the delimiters of the regular expression; that is, element 0 of the array that is returned in list context.

Optionally, you can pass an index value and the corresponding delimiters will be returned; index 0 represents the regular expression's delimiters, and index 1 represents the replacement string's delimiters, which may be undef. For example,

 print PPIx::Regexp->new('s{foo}<bar>')->delimiters(1);
 # prints '<>'

If the object was not initialized with a valid regexp of some sort, the results of this method are undefined.

errstr¶

This static method returns the error string from the most recent attempt to instantiate a "PPIx::Regexp". It will be "undef" if the most recent attempt succeeded.

extract_regexps¶

 my $doc = PPI::Document->new( $path );
 $doc->index_locations();
 my @res = PPIx::Regexp->extract_regexps( $doc )

This convenience (well, sort-of) static method takes as its argument a PPI::Document object and returns "PPIx::Regexp" objects corresponding to all regular expressions found in it, in the order in which they occur in the document. You will need to keep a reference to the original PPI::Document object if you wish to be able to recover the original PPI::Element objects via the PPIx::Regexp source() method.

failures¶

 print "There were ", $re->failures(), " parse failures\n";

This method returns the number of parse failures. This is a count of the number of unknown tokens plus the number of unterminated structures plus the number of unmatched right brackets of any sort.

max_capture_number¶

 print "Highest used capture number ",
     $re->max_capture_number(), "\n";

This convenience method returns the highest capture number used by the regular expression. If there are no captures, the return will be 0.

This method is equivalent to

 $self->regular_expression()->max_capture_number();

except that if "$self->regular_expression()" returns "undef" (meaning that something went terribly wrong with the parse) this method will too.

modifier¶

 my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
 print $re->modifier()->content(), "\n";
 # prints 'smx'.

This method retrieves the modifier of the object. This comes from the end of the initializing string or object and will be a PPIx::Regexp::Token::Modifier.

Note that this object represents the actual modifiers present on the regexp, and does not take into account any that may have been applied by default (i.e. via the "default_modifiers" argument to "new()"). For something that takes account of default modifiers, see modifier_asserted(), below.

In the event of a parse failure, there may not be a modifier present, in which case nothing is returned.

modifier_asserted¶

 my $re = PPIx::Regexp->new( '/ . /',
     default_modifiers => [ 'smx' ] );
 print $re->modifier_asserted( 'x' ) ? "yes\n" : "no\n";
 # prints 'yes'.

This method returns true if the given modifier is asserted for the regexp, whether explicitly or by the modifiers passed in the "default_modifiers" argument.

Starting with version 0.036_01, if the argument is a single-character modifier followed by an asterisk (intended as a wild card character), the return is the number of times that modifier appears. In this case an exception will be thrown if you specify a multi-character modifier (e.g. 'ee*'), or if you specify one of the match semantics modifiers (e.g. 'a*').

regular_expression¶

 my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
 print $re->regular_expression()->content(), "\n";
 # prints '/(foo)/'.

This method returns that portion of the object which actually represents a regular expression.

replacement¶

 my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
 print $re->replacement()->content(), "\n";
 # prints '${1}bar/'.

This method returns that portion of the object which represents the replacement string. This will be "undef" unless the regular expression actually has a replacement string. Delimiters will be included, but there will be no beginning delimiter unless the regular expression was bracketed.

source¶

 my $source = $re->source();

This method returns the object or string that was used to instantiate the object.

type¶

 my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
 print $re->type()->content(), "\n";
 # prints 's'.

This method retrieves the type of the object. This comes from the beginning of the initializing string or object, and will be a PPIx::Regexp::Token::Structure whose "content" is one of 's', 'm', 'qr', or ''.

Ambiguous Syntax¶

Perl's regular expressions contain cases where the syntax is ambiguous. A particularly egregious example is an interpolation followed by square or curly brackets, for example $foo[...]. There is nothing in the syntax to say whether the programmer wanted to interpolate an element of array @foo, or whether he wanted to interpolate scalar $foo, and then follow that interpolation by a character class.

The perlop documentation notes that in this case what Perl does is to guess. That is, it employs various heuristics on the code to try to figure out what the programmer wanted. These heuristics are documented as being undocumented (!) and subject to change without notice. As an example of the problems even perl faces in parsing Perl, see <https://github.com/perl/perl5/issues/16478>.

Given this situation, this module's chances of duplicating every Perl version's interpretation of every regular expression are pretty much nil. What it does now is to assume that square brackets containing only an integer or an interpolation represent a subscript; otherwise they represent a character class. Similarly, curly brackets containing only a bareword or an interpolation are a subscript; otherwise they represent a quantifier.

Changes in Syntax¶

Sometimes the introduction of new syntax changes the way a regular expression is parsed. For example, the "\v" character class was introduced in Perl 5.9.5. But it did not represent a syntax error prior to that version of Perl, it was simply parsed as "v". So

 $ perl -le 'print "v" =~ m/\v/ ? "yes" : "no"'

prints "yes" under Perl 5.8.9, but "no" under 5.10.0. "PPIx::Regexp" generally assumes the more modern parse in cases like this.

Equivocation¶

Very occasionally, a construction will be removed and then added back -- and then, conceivably, removed again. In this case, the plan is for perl_version_introduced() to return the earliest version in which the construction appeared, and perl_version_removed() to return the version after the last version in which it appeared (whether production or development), or "undef" if it is in the highest-numbered Perl.

The constructions involved in this are:

Un-escaped literal left curly after literal

That is, something like "qr<x{>".

This was made an error in 5.25.1, and it was an error in 5.26.0. But it became a warning again in 5.27.1. The perl5271delta says it was re-instated because the changes broke GNU Autoconf, and the warning message says it will be removed in Perl 5.30.

Accordingly, perl_version_introduced() returns 5.0. At the moment perl_version_removed() returns '5.025001'. But if it is present with or without warning in 5.28, perl_version_removed() will become "undef". If you need finer resolution than this, see PPIx::Regexp::Element methods l<accepts_perl()|PPIx::Regexp::Element/accepts_perl> and l<requirements_for_perl()|PPIx::Regexp::Element/requirements_for_perl>

Static Parsing¶

It is well known that Perl can not be statically parsed. That is, you can not completely parse a piece of Perl code without executing that same code.

Nevertheless, this class is trying to statically parse regular expressions. The main problem with this is that there is no way to know what is being interpolated into the regular expression by an interpolated variable. This is a problem because the interpolated value can change the interpretation of adjacent elements.

This module deals with this by making assumptions about what is in an interpolated variable. These assumptions will not be enumerated here, but in general the principal is to assume the interpolated value does not change the interpretation of the regular expression. For example,

 my $foo = 'a-z]';
 my $re = qr{[$foo};

is fine with the Perl interpreter, but will confuse the dickens out of this module. Similarly and more usefully, something like

 my $mods = 'i';
 my $re = qr{(?$mods:foo)};

or maybe

 my $mods = 'i';
 my $re = qr{(?$mods)$foo};

probably sets a modifier of some sort, and that is how this module interprets it. If the interpolation is not about modifiers, this module will get it wrong. Another such semi-benign example is

 my $foo = $] >= 5.010 ? '?<foo>' : '';
 my $re = qr{($foo\w+)};

which will parse, but this module will never realize that it might be looking at a named capture.

Non-Standard Syntax¶

There are modules out there that alter the syntax of Perl. If the syntax of a regular expression is altered, this module has no way to understand that it has been altered, much less to adapt to the alteration. The following modules are known to cause problems:

Acme::PerlML, which renders Perl as XML.

"Data::PostfixDeref", which causes Perl to interpret suffixed empty brackets as dereferencing the thing they suffix. This module by Ben Morrow ("BMORROW") appears to have been retracted.

Filter::Trigraph, which recognizes ANSI C trigraphs, allowing Perl to be written in the ISO 646 character set.

Perl6::Pugs. Enough said.

Perl6::Rules, which back-ports some of the Perl 6 regular expression syntax to Perl 5.

Regexp::Extended, which extends regular expressions in various ways, some of which seem to conflict with Perl 5.010.