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32 .\" @(#)regex.3 8.4 (Berkeley) 3/20/94
43 .Nd regular-expression library
50 .Fa "regex_t * restrict preg" "const char * restrict pattern" "int cflags"
54 .Fa "const regex_t * restrict preg" "const char * restrict string"
55 .Fa "size_t nmatch" "regmatch_t pmatch[restrict]" "int eflags"
59 .Fa "int errcode" "const regex_t * restrict preg"
60 .Fa "char * restrict errbuf" "size_t errbuf_size"
63 .Fn regfree "regex_t *preg"
65 These routines implement
74 compiles an RE written as a string into an internal form,
76 matches that internal form against a string and reports results,
78 transforms error codes from either into human-readable messages,
81 frees any dynamically-allocated storage used by the internal form
86 declares two structure types,
90 the former for compiled internal forms and the latter for match reporting.
91 It also declares the four functions,
94 and a number of constants with names starting with
100 compiles the regular expression contained in the
103 subject to the flags in
105 and places the results in the
107 structure pointed to by
112 is the bitwise OR of zero or more of the following flags:
113 .Bl -tag -width REG_EXTENDED
118 rather than the obsolete
123 This is a synonym for 0,
124 provided as a counterpart to
126 to improve readability.
128 Compile with recognition of all special characters turned off.
129 All characters are thus considered ordinary,
133 This is an extension,
134 compatible with but not specified by
136 and should be used with
137 caution in software intended to be portable to other systems.
145 Compile for matching that ignores upper/lower case distinctions.
149 Compile for matching that need only report success or failure,
150 not what was matched.
152 Compile for newline-sensitive matching.
153 By default, newline is a completely ordinary character with no special
154 meaning in either REs or strings.
157 bracket expressions and
162 anchor matches the null string after any newline in the string
163 in addition to its normal function,
166 anchor matches the null string before any newline in the
167 string in addition to its normal function.
169 The regular expression ends,
170 not at the first NUL,
171 but just before the character pointed to by the
173 member of the structure pointed to by
179 This flag permits inclusion of NULs in the RE;
180 they are considered ordinary characters.
181 This is an extension,
182 compatible with but not specified by
184 and should be used with
185 caution in software intended to be portable to other systems.
190 returns 0 and fills in the structure pointed to by
192 One member of that structure
199 contains the number of parenthesized subexpressions within the RE
200 (except that the value of this member is undefined if the
205 fails, it returns a non-zero error code;
212 matches the compiled RE pointed to by
216 subject to the flags in
218 and reports results using
221 and the returned value.
222 The RE must have been compiled by a previous invocation of
224 The compiled form is not altered during execution of
226 so a single compiled RE can be used simultaneously by multiple threads.
229 the NUL-terminated string pointed to by
231 is considered to be the text of an entire line, minus any terminating
235 argument is the bitwise OR of zero or more of the following flags:
236 .Bl -tag -width REG_STARTEND
238 The first character of the string is treated as the continuation
240 This means that the anchors
245 do not match before it; but see
248 This does not affect the behavior of newlines under
253 does not end a line, so the
255 anchor does not match before it.
256 This does not affect the behavior of newlines under
259 The string is considered to start at
261 .Fa pmatch Ns [0]. Ns Fa rm_so
262 and to end before the byte located at
264 .Fa pmatch Ns [0]. Ns Fa rm_eo ,
265 regardless of the value of
267 See below for the definition of
271 This is an extension,
272 compatible with but not specified by
274 and should be used with
275 caution in software intended to be portable to other systems.
281 is considered the beginning of a line, such that
283 matches before it, and the beginning of a word if there is a word
284 character at this position, such that
292 the character at position
294 is treated as the continuation of a line, and if
296 is greater than 0, the preceding character is taken into consideration.
297 If the preceding character is a newline and the regular expression was compiled
301 matches before the string; if the preceding character is not a word character
302 but the string starts with a word character,
306 match before the string.
311 for a discussion of what is matched in situations where an RE or a
312 portion thereof could match any of several substrings of
317 returns 0 for success and the non-zero code
320 Other non-zero error codes may be returned in exceptional situations;
326 was specified in the compilation of the RE,
333 argument (but see below for the case where
338 points to an array of
342 Such a structure has at least the members
348 (a signed arithmetic type at least as large as an
352 containing respectively the offset of the first character of a substring
353 and the offset of the first character after the end of the substring.
354 Offsets are measured from the beginning of the
358 An empty substring is denoted by equal offsets,
359 both indicating the character following the empty substring.
361 The 0th member of the
363 array is filled in to indicate what substring of
365 was matched by the entire RE.
366 Remaining members report what substring was matched by parenthesized
367 subexpressions within the RE;
370 reports subexpression
372 with subexpressions counted (starting at 1) by the order of their opening
373 parentheses in the RE, left to right.
374 Unused entries in the array (corresponding either to subexpressions that
375 did not participate in the match at all, or to subexpressions that do not
376 exist in the RE (that is,
379 .Fa preg Ns -> Ns Va re_nsub ) )
385 If a subexpression participated in the match several times,
386 the reported substring is the last one it matched.
387 (Note, as an example in particular, that when the RE
391 the parenthesized subexpression matches each of the three
394 an infinite number of empty strings following the last
396 so the reported substring is one of the empties.)
402 must point to at least one
409 to hold the input offsets for
411 Use for output is still entirely controlled by
420 will not be changed by a successful
432 to a human-readable, printable message.
436 .No non\- Ns Dv NULL ,
437 the error code should have arisen from use of
442 and if the error code came from
444 it should have been the result from the most recent
451 may be able to supply a more detailed message using information
458 places the NUL-terminated message into the buffer pointed to by
460 limiting the length (including the NUL) to at most
463 If the whole message will not fit,
464 as much of it as will fit before the terminating NUL is supplied.
466 the returned value is the size of buffer needed to hold the whole
467 message (including terminating NUL).
472 is ignored but the return value is still correct.
482 that results is the printable name of the error code,
485 rather than an explanation thereof.
496 member of the structure it points to
497 must point to the printable name of an error code;
498 in this case, the result in
500 is the decimal digits of
501 the numeric value of the error code
502 (0 if the name is not recognized).
506 are intended primarily as debugging facilities;
508 compatible with but not specified by
510 and should be used with
511 caution in software intended to be portable to other systems.
512 Be warned also that they are considered experimental and changes are possible.
517 frees any dynamically-allocated storage associated with the compiled RE
522 is no longer a valid compiled RE
523 and the effect of supplying it to
529 None of these functions references global variables except for tables
531 all are safe for use from multiple threads if the arguments are safe.
532 .Sh IMPLEMENTATION CHOICES
533 There are a number of decisions that
535 leaves up to the implementor,
536 either by explicitly saying
538 or by virtue of them being
539 forbidden by the RE grammar.
540 This implementation treats them as follows.
544 for a discussion of the definition of case-independent matching.
546 There is no particular limit on the length of REs,
547 except insofar as memory is limited.
548 Memory usage is approximately linear in RE size, and largely insensitive
549 to RE complexity, except for bounded repetitions.
552 for one short RE using them
553 that will run almost any system out of memory.
555 A backslashed character other than one specifically given a magic meaning
558 (such magic meanings occur only in obsolete
561 is taken as an ordinary character.
569 Equivalence classes cannot begin or end bracket-expression ranges.
570 The endpoint of one range cannot begin another.
573 the limit on repetition counts in bounded repetitions, is 255.
575 A repetition operator
580 cannot follow another
582 A repetition operator cannot begin an expression or subexpression
589 cannot appear first or last in a (sub)expression or after another
593 cannot be an empty subexpression.
594 An empty parenthesized subexpression,
596 is legal and matches an
598 An empty string is not a legal RE.
602 followed by a digit is considered the beginning of bounds for a
603 bounded repetition, which must then follow the syntax for bounds.
607 followed by a digit is considered an ordinary character.
612 beginning and ending subexpressions in obsolete
614 REs are anchors, not ordinary characters.
616 Non-zero error codes from
620 include the following:
622 .Bl -tag -width REG_ECOLLATE -compact
629 invalid regular expression
631 invalid collating element
633 invalid character class
636 applied to unescapable character
638 invalid backreference number
652 invalid repetition count(s) in
655 invalid character range in
666 empty (sub)expression
668 cannot happen - you found a bug
670 invalid argument, e.g.\& negative-length string
672 illegal byte sequence (bad multibyte character)
679 sections 2.8 (Regular Expression Notation)
681 B.5 (C Binding for Regular Expression Matching).
683 Originally written by
685 Altered for inclusion in the
689 This is an alpha release with known defects.
690 Please report problems.
692 The back-reference code is subtle and doubts linger about its correctness
699 This will improve with later releases.
703 exceeding 0 is expensive;
705 exceeding 1 is worse.
709 is largely insensitive to RE complexity
712 references are massively expensive.
713 RE length does matter; in particular, there is a strong speed bonus
714 for keeping RE length under about 30 characters,
715 with most special characters counting roughly double.
720 implements bounded repetitions by macro expansion,
721 which is costly in time and space if counts are large
722 or bounded repetitions are nested.
724 .Ql "((((a{1,100}){1,100}){1,100}){1,100}){1,100}"
725 will (eventually) run almost any existing machine out of swap space.
727 There are suspected problems with response to obscure error conditions.
729 certain kinds of internal overflow,
730 produced only by truly enormous REs or by multiply nested bounded repetitions,
731 are probably not handled well.
737 are legal REs because
740 a special character only in the presence of a previous unmatched
742 This cannot be fixed until the spec is fixed.
744 The standard's definition of back references is vague.
746 .Ql "a\e(\e(b\e)*\e2\e)*d"
749 Until the standard is clarified,
750 behavior in such cases should not be relied on.
752 The implementation of word-boundary matching is a bit of a kludge,
753 and bugs may lurk in combinations of word-boundary matching and anchoring.
755 Word-boundary matching does not work properly in multibyte locales.
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