3 perlreapi - perl regular expression plugin interface
7 As of Perl 5.9.5 there is a new interface for using other regexp
8 engines than the default one. Each engine is supposed to provide
9 access to a constant structure of the following format:
11 typedef struct regexp_engine {
12 REGEXP* (*comp) (pTHX_ const SV * const pattern, const U32 flags);
13 I32 (*exec) (pTHX_ REGEXP * const rx, char* stringarg, char* strend,
14 char* strbeg, I32 minend, SV* screamer,
15 void* data, U32 flags);
16 char* (*intuit) (pTHX_ REGEXP * const rx, SV *sv, char *strpos,
17 char *strend, U32 flags,
18 struct re_scream_pos_data_s *data);
19 SV* (*checkstr) (pTHX_ REGEXP * const rx);
20 void (*free) (pTHX_ REGEXP * const rx);
21 void (*numbered_buff_FETCH) (pTHX_ REGEXP * const rx, const I32 paren,
23 void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren,
24 SV const * const value);
25 I32 (*numbered_buff_LENGTH) (pTHX_ REGEXP * const rx, const SV * const sv,
27 SV* (*named_buff) (pTHX_ REGEXP * const rx, SV * const key,
28 SV * const value, U32 flags);
29 SV* (*named_buff_iter) (pTHX_ REGEXP * const rx, const SV * const lastkey,
31 SV* (*qr_package)(pTHX_ REGEXP * const rx);
33 void* (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
36 When a regexp is compiled, its C<engine> field is then set to point at
37 the appropriate structure so that when it needs to be used Perl can find
38 the right routines to do so.
40 In order to install a new regexp handler, C<$^H{regcomp}> is set
41 to an integer which (when casted appropriately) resolves to one of these
42 structures. When compiling, the C<comp> method is executed, and the
43 resulting regexp structure's engine field is expected to point back at
46 The pTHX_ symbol in the definition is a macro used by perl under threading
47 to provide an extra argument to the routine holding a pointer back to
48 the interpreter that is executing the regexp. So under threading all
49 routines get an extra argument.
55 REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags);
57 Compile the pattern stored in C<pattern> using the given C<flags> and
58 return a pointer to a prepared C<REGEXP> structure that can perform
59 the match. See L</The REGEXP structure> below for an explanation of
60 the individual fields in the REGEXP struct.
62 The C<pattern> parameter is the scalar that was used as the
63 pattern. previous versions of perl would pass two C<char*> indicating
64 the start and end of the stringifed pattern, the following snippet can
65 be used to get the old parameters:
68 char* exp = SvPV(pattern, plen);
69 char* xend = exp + plen;
71 Since any scalar can be passed as a pattern it's possible to implement
72 an engine that does something with an array (C<< "ook" =~ [ qw/ eek
73 hlagh / ] >>) or with the non-stringified form of a compiled regular
74 expression (C<< "ook" =~ qr/eek/ >>). perl's own engine will always
75 stringify everything using the snippet above but that doesn't mean
76 other engines have to.
78 The C<flags> paramater is a bitfield which indicates which of the
79 C<msixp> flags the regex was compiled with. It also contains
80 additional info such as whether C<use locale> is in effect.
82 The C<eogc> flags are stripped out before being passed to the comp
83 routine. The regex engine does not need to know whether any of these
84 are set as those flags should only affect what perl does with the
85 pattern and its match variables, not how it gets compiled and
88 By the time the comp callback is called, some of these flags have
89 already had effect (noted below where applicable). However most of
90 their effect occurs after the comp callback has run in routines that
91 read the C<< rx->extflags >> field which it populates.
93 In general the flags should be preserved in C<< rx->extflags >> after
94 compilation, although the regex engine might want to add or delete
95 some of them to invoke or disable some special behavior in perl. The
96 flags along with any special behavior they cause are documented below:
98 The pattern modifiers:
102 =item C</m> - RXf_PMf_MULTILINE
104 If this is in C<< rx->extflags >> it will be passed to
105 C<Perl_fbm_instr> by C<pp_split> which will treat the subject string
106 as a multi-line string.
108 =item C</s> - RXf_PMf_SINGLELINE
110 =item C</i> - RXf_PMf_FOLD
112 =item C</x> - RXf_PMf_EXTENDED
114 If present on a regex C<#> comments will be handled differently by the
115 tokenizer in some cases.
117 TODO: Document those cases.
119 =item C</p> - RXf_PMf_KEEPCOPY
129 If C<split> is invoked as C<split ' '> or with no arguments (which
130 really means C<split(' ', $_>, see L<split|perlfunc/split>), perl will set
131 this flag and change the pattern from C<" "> to C<"\s+"> before it's
132 passed to the comp routine.
134 If the flag is present in C<< rx->extflags >> C<split> to delete
135 whitespace from the start of the subject string before it's operated
136 on. What is considered whitespace depends on whether the subject is a
137 UTF-8 string and whether the C<RXf_PMf_LOCALE> flag is set.
139 This probably always be preserved verbatim in C<< rx->extflags >>.
143 Set if C<use locale> is in effect. If present in C<< rx->extflags >>
144 C<split> will use the locale dependant definition of whitespace under
145 when RXf_SKIPWHITE or RXf_WHITE are in effect. Under ASCII whitespace
146 is defined as per L<isSPACE|perlapi/ISSPACE>, and by the internal
147 macros C<is_utf8_space> under UTF-8 and C<isSPACE_LC> under C<use
152 Set if the pattern is L<SvUTF8()|perlapi/SvUTF8>, set by Perl_pmruntime.
154 A regex engine may want to set or disable this flag during
155 compilation. The perl engine for instance may upgrade non-UTF-8
156 strings to UTF-8 if the pattern includes constructs such as C<\x{...}>
157 that can only match Unicode values.
161 These flags can be set during compilation to enable optimizations in
162 the C<split> operator.
168 Tells the split operator to split the target string on newlines
169 (C<\n>) without invoking the regex engine.
171 Perl's engine sets this if the pattern is C</^/> (C<plen == 1 && *exp
172 == '^'>), even under C</^/s>, see L<split|perlfunc>. Of course a
173 different regex engine might want to use the same optimizations
174 with a different syntax.
178 Tells the split operator to split the target string on whitespace
179 without invoking the regex engine. The definition of whitespace varies
180 depending on whether the target string is a UTF-8 string and on
181 whether RXf_PMf_LOCALE is set.
183 Perl's engine sets this flag if the pattern is C<\s+>, which it will be if
184 the pattern actually was C<\s+> or if it was originally C<" "> (see
185 C<RXf_SKIPWHITE> above).
191 I32 exec(pTHX_ REGEXP * const rx,
192 char *stringarg, char* strend, char* strbeg,
193 I32 minend, SV* screamer,
194 void* data, U32 flags);
200 char* intuit(pTHX_ REGEXP * const rx,
201 SV *sv, char *strpos, char *strend,
202 const U32 flags, struct re_scream_pos_data_s *data);
204 Find the start position where a regex match should be attempted,
205 or possibly whether the regex engine should not be run because the
206 pattern can't match. This is called as appropriate by the core
207 depending on the values of the extflags member of the regexp
212 SV* checkstr(pTHX_ REGEXP * const rx);
214 Return a SV containing a string that must appear in the pattern. Used
215 by C<split> for optimising matches.
219 void free(pTHX_ REGEXP * const rx);
221 Called by perl when it is freeing a regexp pattern so that the engine
222 can release any resources pointed to by the C<pprivate> member of the
223 regexp structure. This is only responsible for freeing private data;
224 perl will handle releasing anything else contained in the regexp structure.
226 =head2 Numbered capture callbacks
228 Called to get/set the value of C<$`>, C<$'>, C<$&> and their named
229 equivalents, ${^PREMATCH}, ${^POSTMATCH} and $^{MATCH}, as well as the
230 numbered capture buffers (C<$1>, C<$2>, ...).
232 The C<paren> paramater will be C<-2> for C<$`>, C<-1> for C<$'>, C<0>
233 for C<$&>, C<1> for C<$1> and so forth.
235 The names have been chosen by analogy with L<Tie::Scalar> methods
236 names with an additional B<LENGTH> callback for efficiency. However
237 named capture variables are currently not tied internally but
238 implemented via magic.
240 =head3 numbered_buff_FETCH
242 void numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren,
245 Fetch a specified numbered capture. C<sv> should be set to the scalar
246 to return, the scalar is passed as an argument rather than being
247 returned from the function because when it's called perl already has a
248 scalar to store the value, creating another one would be
249 redundant. The scalar can be set with C<sv_setsv>, C<sv_setpvn> and
250 friends, see L<perlapi>.
252 This callback is where perl untaints its own capture variables under
253 taint mode (see L<perlsec>). See the C<Perl_reg_numbered_buff_fetch>
254 function in F<regcomp.c> for how to untaint capture variables if
255 that's something you'd like your engine to do as well.
257 =head3 numbered_buff_STORE
259 void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren,
260 SV const * const value);
262 Set the value of a numbered capture variable. C<value> is the scalar
263 that is to be used as the new value. It's up to the engine to make
264 sure this is used as the new value (or reject it).
268 if ("ook" =~ /(o*)/) {
269 # `paren' will be `1' and `value' will be `ee'
273 Perl's own engine will croak on any attempt to modify the capture
274 variables, to do this in another engine use the following callack
275 (copied from C<Perl_reg_numbered_buff_store>):
278 Example_reg_numbered_buff_store(pTHX_ REGEXP * const rx, const I32 paren,
279 SV const * const value)
282 PERL_UNUSED_ARG(paren);
283 PERL_UNUSED_ARG(value);
286 Perl_croak(aTHX_ PL_no_modify);
289 Actually perl 5.10 will not I<always> croak in a statement that looks
290 like it would modify a numbered capture variable. This is because the
291 STORE callback will not be called if perl can determine that it
292 doesn't have to modify the value. This is exactly how tied variables
293 behave in the same situation:
296 use base 'Tie::Scalar';
298 sub TIESCALAR { bless [] }
300 sub STORE { die "This doesn't get called" }
304 tie my $sv => "CatptureVar";
307 Because C<$sv> is C<undef> when the C<y///> operator is applied to it
308 the transliteration won't actually execute and the program won't
309 C<die>. This is different to how 5.8 and earlier versions behaved
310 since the capture variables were READONLY variables then, now they'll
311 just die when assigned to in the default engine.
313 =head3 numbered_buff_LENGTH
315 I32 numbered_buff_LENGTH (pTHX_ REGEXP * const rx, const SV * const sv,
318 Get the C<length> of a capture variable. There's a special callback
319 for this so that perl doesn't have to do a FETCH and run C<length> on
320 the result, since the length is (in perl's case) known from an offset
321 stored in C<<rx->offs> this is much more efficient:
323 I32 s1 = rx->offs[paren].start;
324 I32 s2 = rx->offs[paren].end;
327 This is a little bit more complex in the case of UTF-8, see what
328 C<Perl_reg_numbered_buff_length> does with
329 L<is_utf8_string_loclen|perlapi/is_utf8_string_loclen>.
331 =head2 Named capture callbacks
333 Called to get/set the value of C<%+> and C<%-> as well as by some
334 utility functions in L<re>.
336 There are two callbacks, C<named_buff> is called in all the cases the
337 FETCH, STORE, DELETE, CLEAR, EXISTS and SCALAR L<Tie::Hash> callbacks
338 would be on changes to C<%+> and C<%-> and C<named_buff_iter> in the
339 same cases as FIRSTKEY and NEXTKEY.
341 The C<flags> parameter can be used to determine which of these
342 operations the callbacks should respond to, the following flags are
345 Which L<Tie::Hash> operation is being performed from the Perl level on
346 C<%+> or C<%+>, if any:
357 Whether C<%+> or C<%-> is being operated on, if any.
359 RXf_HASH_ONE /* %+ */
360 RXf_HASH_ALL /* %- */
362 Whether this is being called as C<re::regname>, C<re::regnames> or
363 C<re::regnames_count>, if any. The first two will be combined with
364 C<RXf_HASH_ONE> or C<RXf_HASH_ALL>.
368 RXf_HASH_REGNAMES_COUNT
370 Internally C<%+> and C<%-> are implemented with a real tied interface
371 via L<Tie::Hash::NamedCapture>. The methods in that package will call
372 back into these functions. However the usage of
373 L<Tie::Hash::NamedCapture> for this purpose might change in future
374 releases. For instance this might be implemented by magic instead
375 (would need an extension to mgvtbl).
379 SV* (*named_buff) (pTHX_ REGEXP * const rx, SV * const key,
380 SV * const value, U32 flags);
382 =head3 named_buff_iter
384 SV* (*named_buff_iter) (pTHX_ REGEXP * const rx, const SV * const lastkey,
389 SV* qr_package(pTHX_ REGEXP * const rx);
391 The package the qr// magic object is blessed into (as seen by C<ref
392 qr//>). It is recommended that engines change this to their package
393 name for identification regardless of whether they implement methods
396 The package this method returns should also have the internal
397 C<Regexp> package in its C<@ISA>. C<qr//->isa("Regexp")> should always
398 be true regardless of what engine is being used.
400 Example implementation might be:
403 Example_qr_package(pTHX_ REGEXP * const rx)
406 return newSVpvs("re::engine::Example");
409 Any method calls on an object created with C<qr//> will be dispatched to the
410 package as a normal object.
412 use re::engine::Example;
414 $re->meth; # dispatched to re::engine::Example::meth()
416 To retrieve the C<REGEXP> object from the scalar in an XS function use
417 the C<SvRX> macro, see L<"REGEXP Functions" in perlapi|perlapi/REGEXP
422 REGEXP * re = SvRX(sv);
426 void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
428 On threaded builds a regexp may need to be duplicated so that the pattern
429 can be used by mutiple threads. This routine is expected to handle the
430 duplication of any private data pointed to by the C<pprivate> member of
431 the regexp structure. It will be called with the preconstructed new
432 regexp structure as an argument, the C<pprivate> member will point at
433 the B<old> private structue, and it is this routine's responsibility to
434 construct a copy and return a pointer to it (which perl will then use to
435 overwrite the field as passed to this routine.)
437 This allows the engine to dupe its private data but also if necessary
438 modify the final structure if it really must.
440 On unthreaded builds this field doesn't exist.
442 =head1 The REGEXP structure
444 The REGEXP struct is defined in F<regexp.h>. All regex engines must be able to
445 correctly build such a structure in their L</comp> routine.
447 The REGEXP structure contains all the data that perl needs to be aware of
448 to properly work with the regular expression. It includes data about
449 optimisations that perl can use to determine if the regex engine should
450 really be used, and various other control info that is needed to properly
451 execute patterns in various contexts such as is the pattern anchored in
452 some way, or what flags were used during the compile, or whether the
453 program contains special constructs that perl needs to be aware of.
455 In addition it contains two fields that are intended for the private
456 use of the regex engine that compiled the pattern. These are the
457 C<intflags> and C<pprivate> members. C<pprivate> is a void pointer to
458 an arbitrary structure whose use and management is the responsibility
459 of the compiling engine. perl will never modify either of these
462 typedef struct regexp {
463 /* what engine created this regexp? */
464 const struct regexp_engine* engine;
466 /* what re is this a lightweight copy of? */
467 struct regexp* mother_re;
469 /* Information about the match that the perl core uses to manage things */
470 U32 extflags; /* Flags used both externally and internally */
471 I32 minlen; /* mininum possible length of string to match */
472 I32 minlenret; /* mininum possible length of $& */
473 U32 gofs; /* chars left of pos that we search from */
475 /* substring data about strings that must appear
476 in the final match, used for optimisations */
477 struct reg_substr_data *substrs;
479 U32 nparens; /* number of capture buffers */
481 /* private engine specific data */
482 U32 intflags; /* Engine Specific Internal flags */
483 void *pprivate; /* Data private to the regex engine which
484 created this object. */
486 /* Data about the last/current match. These are modified during matching*/
487 U32 lastparen; /* last open paren matched */
488 U32 lastcloseparen; /* last close paren matched */
489 regexp_paren_pair *swap; /* Swap copy of *offs */
490 regexp_paren_pair *offs; /* Array of offsets for (@-) and (@+) */
492 char *subbeg; /* saved or original string so \digit works forever. */
493 SV_SAVED_COPY /* If non-NULL, SV which is COW from original */
494 I32 sublen; /* Length of string pointed by subbeg */
496 /* Information about the match that isn't often used */
497 I32 prelen; /* length of precomp */
498 const char *precomp; /* pre-compilation regular expression */
500 char *wrapped; /* wrapped version of the pattern */
501 I32 wraplen; /* length of wrapped */
503 I32 seen_evals; /* number of eval groups in the pattern - for security checks */
504 HV *paren_names; /* Optional hash of paren names */
506 /* Refcount of this regexp */
507 I32 refcnt; /* Refcount of this regexp */
510 The fields are discussed in more detail below:
514 This field points at a regexp_engine structure which contains pointers
515 to the subroutines that are to be used for performing a match. It
516 is the compiling routine's responsibility to populate this field before
517 returning the regexp object.
519 Internally this is set to C<NULL> unless a custom engine is specified in
520 C<$^H{regcomp}>, perl's own set of callbacks can be accessed in the struct
521 pointed to by C<RE_ENGINE_PTR>.
525 TODO, see L<http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html>
529 This will be used by perl to see what flags the regexp was compiled
530 with, this will normally be set to the value of the flags parameter by
531 the L<comp|/comp> callback. See the L<comp|/comp> documentation for
534 =head2 C<minlen> C<minlenret>
536 The minimum string length required for the pattern to match. This is used to
537 prune the search space by not bothering to match any closer to the end of a
538 string than would allow a match. For instance there is no point in even
539 starting the regex engine if the minlen is 10 but the string is only 5
540 characters long. There is no way that the pattern can match.
542 C<minlenret> is the minimum length of the string that would be found
545 The difference between C<minlen> and C<minlenret> can be seen in the
550 where the C<minlen> would be 3 but C<minlenret> would only be 2 as the \d is
551 required to match but is not actually included in the matched content. This
552 distinction is particularly important as the substitution logic uses the
553 C<minlenret> to tell whether it can do in-place substition which can result in
554 considerable speedup.
558 Left offset from pos() to start match at.
562 Substring data about strings that must appear in the final match. This
563 is currently only used internally by perl's engine for but might be
564 used in the future for all engines for optimisations.
566 =head2 C<nparens>, C<lasparen>, and C<lastcloseparen>
568 These fields are used to keep track of how many paren groups could be matched
569 in the pattern, which was the last open paren to be entered, and which was
570 the last close paren to be entered.
574 The engine's private copy of the flags the pattern was compiled with. Usually
575 this is the same as C<extflags> unless the engine chose to modify one of them.
579 A void* pointing to an engine-defined data structure. The perl engine uses the
580 C<regexp_internal> structure (see L<perlreguts/Base Structures>) but a custom
581 engine should use something else.
589 A C<regexp_paren_pair> structure which defines offsets into the string being
590 matched which correspond to the C<$&> and C<$1>, C<$2> etc. captures, the
591 C<regexp_paren_pair> struct is defined as follows:
593 typedef struct regexp_paren_pair {
598 If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that
599 capture buffer did not match. C<< ->offs[0].start/end >> represents C<$&> (or
600 C<${^MATCH> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where
603 =head2 C<precomp> C<prelen>
605 Used for optimisations. C<precomp> holds a copy of the pattern that
606 was compiled and C<prelen> its length. When a new pattern is to be
607 compiled (such as inside a loop) the internal C<regcomp> operator
608 checks whether the last compiled C<REGEXP>'s C<precomp> and C<prelen>
609 are equivalent to the new one, and if so uses the old pattern instead
610 of compiling a new one.
612 The relevant snippet from C<Perl_pp_regcomp>:
614 if (!re || !re->precomp || re->prelen != (I32)len ||
615 memNE(re->precomp, t, len))
616 /* Compile a new pattern */
618 =head2 C<paren_names>
620 This is a hash used internally to track named capture buffers and their
621 offsets. The keys are the names of the buffers the values are dualvars,
622 with the IV slot holding the number of buffers with the given name and the
623 pv being an embedded array of I32. The values may also be contained
624 independently in the data array in cases where named backreferences are
629 Holds information on the longest string that must occur at a fixed
630 offset from the start of the pattern, and the longest string that must
631 occur at a floating offset from the start of the pattern. Used to do
632 Fast-Boyer-Moore searches on the string to find out if its worth using
633 the regex engine at all, and if so where in the string to search.
635 =head2 C<subbeg> C<sublen> C<saved_copy>
637 Used during execution phase for managing search and replace patterns.
639 =head2 C<wrapped> C<wraplen>
641 Stores the string C<qr//> stringifies to. The perl engine for example
642 stores C<(?-xism:eek)> in the case of C<qr/eek/>.
644 When using a custom engine that doesn't support the C<(?:)> construct
645 for inline modifiers, it's probably best to have C<qr//> stringify to
646 the supplied pattern, note that this will create undesired patterns in
649 my $x = qr/a|b/; # "a|b"
650 my $y = qr/c/i; # "c"
651 my $z = qr/$x$y/; # "a|bc"
653 There's no solution for this problem other than making the custom
654 engine understand a construct like C<(?:)>.
658 This stores the number of eval groups in the pattern. This is used for security
659 purposes when embedding compiled regexes into larger patterns with C<qr//>.
663 The number of times the structure is referenced. When this falls to 0 the
664 regexp is automatically freed by a call to pregfree. This should be set to 1 in
665 each engine's L</comp> routine.
669 Originally part of L<perlreguts>.
673 Originally written by Yves Orton, expanded by E<AElig>var ArnfjE<ouml>rE<eth>
678 Copyright 2006 Yves Orton and 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason.
680 This program is free software; you can redistribute it and/or modify it under
681 the same terms as Perl itself.