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regex(3)                 BSD Library Functions Manual                 regex(3)


NAME

     regcomp, regcomp_l, regerror, regexec, regfree, regncomp, regncomp_l,
     regnexec, regnwcomp, regnwcomp_l, regnwexec, regwcomp, regwcomp_l,
     regwexec -- regular-expression library


SYNOPSIS

     (Standards-compliant APIs)

     #include <regex.h>

     int
     regcomp(regex_t *restrict preg, const char *restrict pattern,
         int cflags);

     size_t
     regerror(int errcode, const regex_t *restrict preg,
         char *restrict errbuf, size_t errbuf_size);

     int
     regexec(const regex_t *restrict preg, const char *restrict string,
         size_t nmatch, regmatch_t pmatch[restrict], int eflags);

     void
     regfree(regex_t *preg);

     (Non-portable extensions)

     int
     regncomp(regex_t *restrict preg, const char *restrict pattern,
         size_t len, int cflags);

     int
     regnexec(const regex_t *restrict preg, const char *restrict string,
         size_t len, size_t nmatch, regmatch_t pmatch[restrict], int eflags);

     int
     regwcomp(regex_t *restrict preg, const wchar_t *restrict widepat,
         int cflags);

     int
     regwexec(const regex_t *restrict preg, const wchar_t *restrict widestr,
         size_t nmatch, regmatch_t pmatch[restrict], int eflags);

     int
     regwncomp(regex_t *restrict preg, const wchar_t *restrict widepat,
         size_t len, int cflags);

     int
     regwnexec(const regex_t *restrict preg, const wchar_t *restrict widestr,
         size_t len, size_t nmatch, regmatch_t pmatch[restrict], int eflags);

     #include <regex.h>
     #include <xlocale.h>

     int
     regcomp_l(regex_t *restrict preg, const char *restrict pattern,
         int cflags, locale_t restrict);

     int
     regncomp_l(regex_t *restrict preg, const char *restrict pattern,
         size_t len, int cflags, locale_t restrict);

     int
     regwcomp_l(regex_t *restrict preg, const wchar_t *restrict widepat,
         int cflags, locale_t restrict);

     int
     regwncomp_l(regex_t *restrict preg, const wchar_t *restrict widepat,
         size_t len, int cflags, locale_t restrict);


DESCRIPTION

     These routines implement IEEE Std 1003.2 (``POSIX.2'') regular expres-
     sions (``RE''s); see re_format(7).  The regcomp() function compiles an
     RE, written as a string, into an internal form.  regexec() matches that
     internal form against a string and reports results.  regerror() trans-
     forms error codes from either into human-readable messages.  regfree()
     frees any dynamically-allocated storage used by the internal form of an
     RE.

     The header <regex.h> declares two structure types, regex_t and
     regmatch_t, the former for compiled internal forms and the latter for
     match reporting.  It also declares the four functions, a type regoff_t,
     and a number of constants with names starting with ``REG_''.

     The regcomp() function compiles the regular expression contained in the
     pattern string, subject to the flags in cflags, and places the results in
     the regex_t structure pointed to by preg.  The cflags argument is the
     bitwise OR of zero or more of the following flags:

     REG_EXTENDED  Compile modern (``extended'') REs, rather than the obsolete
                   (``basic'') REs that are the default.

     REG_BASIC     This is a synonym for 0, provided as a counterpart to
                   REG_EXTENDED to improve readability.

     REG_NOSPEC    Compile with recognition of all special characters turned
                   off.  All characters are thus considered ordinary, so the
                   ``RE'' is a literal string.  This is an extension, compati-
                   ble with but not specified by IEEE Std 1003.2
                   (``POSIX.2''), and should be used with caution in software
                   intended to be portable to other systems.  REG_EXTENDED and
                   REG_NOSPEC may not be used in the same call to regcomp().

     REG_LITERAL   An alias of REG_NOSPEC.

     REG_ICASE     Compile for matching that ignores upper/lower case distinc-
                   tions.  See re_format(7).

     REG_NOSUB     Compile for matching that need only report success or fail-
                   ure, not what was matched.

     REG_NEWLINE   Compile for newline-sensitive matching.  By default, new-
                   line is a completely ordinary character with no special
                   meaning in either REs or strings.  With this flag, `[^'
                   bracket expressions and `.' never match newline, a `^'
                   anchor matches the null string after any newline in the
                   string in addition to its normal function, and the `$'
                   anchor matches the null string before any newline in the
                   string in addition to its normal function.

     REG_PEND      (Note that REG_PEND is not recognized by any of the wide
                   character or ``n'' variants.  Besides, the ``n'' variants
                   can be used instead of REG_PEND; see EXTENDED APIS below.)
                   The regular expression ends, not at the first NUL, but just
                   before the character pointed to by the re_endp member of
                   the structure pointed to by preg.  The re_endp member is of
                   type const char *.  This flag permits inclusion of NULs in
                   the RE; they are considered ordinary characters.  This is
                   an extension, compatible with but not specified by IEEE Std
                   1003.2 (``POSIX.2''), and should be used with caution in
                   software intended to be portable to other systems.

     REG_ENHANCED  Recognized enhanced regular expression features; see
                   re_format(7) for details.  This is an extension not speci-
                   fied by IEEE Std 1003.2 (``POSIX.2''), and should be used
                   with caution in software intended to be portable to other
                   systems.

     REG_MINIMAL   Use minimal (non-greedy) repetitions instead of the normal
                   greedy ones; see re_format(7) for details.  (This only
                   applies when both REG_ENHANCED and REG_EXTENDED are also
                   set.)  This is an extension not specified by IEEE Std
                   1003.2 (``POSIX.2''), and should be used with caution in
                   software intended to be portable to other systems.

     REG_UNGREEDY  Alias of REG_MINIMAL.

     When successful, regcomp() returns 0 and fills in the structure pointed
     to by preg.  One member of that structure (other than re_endp) is publi-
     cized: re_nsub, of type size_t, contains the number of parenthesized
     subexpressions within the RE (except that the value of this member is
     undefined if the REG_NOSUB flag was used).  If regcomp() fails, it
     returns a non-zero error code; see DIAGNOSTICS.

     The regexec() function matches the compiled RE pointed to by preg against
     the string, subject to the flags in eflags, and reports results using
     nmatch, pmatch, and the returned value.  The RE must have been compiled
     by a previous invocation of regcomp().  The compiled form is not altered
     during execution of regexec(), so a single compiled RE can be used simul-
     taneously by multiple threads.

     By default, the NUL-terminated string pointed to by string is considered
     to be the text of an entire line, minus any terminating newline.  The
     eflags argument is the bitwise OR of zero or more of the following flags:

     REG_NOTBOL    The first character of the string is not the beginning of a
                   line, so the `^' anchor should not match before it.  This
                   does not affect the behavior of newlines under REG_NEWLINE.

     REG_NOTEOL    The NUL terminating the string does not end a line, so the
                   `$' anchor should not match before it.  This does not
                   affect the behavior of newlines under REG_NEWLINE.

     REG_STARTEND  The string is considered to start at string +
                   pmatch[0].rm_so and to have a terminating NUL located at
                   string + pmatch[0].rm_eo (there need not actually be a NUL
                   at that location), regardless of the value of nmatch.  See
                   below for the definition of pmatch and nmatch.  This is an
                   extension, compatible with but not specified by IEEE Std
                   1003.2 (``POSIX.2''), and should be used with caution in
                   software intended to be portable to other systems.  Note
                   that a non-zero rm_so does not imply REG_NOTBOL;
                   REG_STARTEND affects only the location of the string, not
                   how it is matched.

     See re_format(7) for a discussion of what is matched in situations where
     an RE or a portion thereof could match any of several substrings of
     string.

     Normally, regexec() returns 0 for success and the non-zero code
     REG_NOMATCH for failure.  Other non-zero error codes may be returned in
     exceptional situations; see DIAGNOSTICS.

     If REG_NOSUB was specified in the compilation of the RE, or if nmatch is
     0, regexec() ignores the pmatch argument (but see below for the case
     where REG_STARTEND is specified).  Otherwise, pmatch points to an array
     of nmatch structures of type regmatch_t.  Such a structure has at least
     the members rm_so and rm_eo, both of type regoff_t (a signed arithmetic
     type at least as large as an off_t and a ssize_t), containing respec-
     tively the offset of the first character of a substring and the offset of
     the first character after the end of the substring.  Offsets are measured
     from the beginning of the string argument given to regexec().  An empty
     substring is denoted by equal offsets, both indicating the character fol-
     lowing the empty substring.

     The 0th member of the pmatch array is filled in to indicate what sub-
     string of string was matched by the entire RE.  Remaining members report
     what substring was matched by parenthesized subexpressions within the RE;
     member i reports subexpression i, with subexpressions counted (starting
     at 1) by the order of their opening parentheses in the RE, left to right.
     Unused entries in the array (corresponding either to subexpressions that
     did not participate in the match at all, or to subexpressions that do not
     exist in the RE (that is, i > preg->re_nsub)) have both rm_so and rm_eo
     set to -1.  If a subexpression participated in the match several times,
     the reported substring is the last one it matched.  (Note, as an example
     in particular, that when the RE `(b*)+' matches `bbb', the parenthesized
     subexpression matches each of the three `b's and then an infinite number
     of empty strings following the last `b', so the reported substring is one
     of the empties.)

     If REG_STARTEND is specified, pmatch must point to at least one
     regmatch_t (even if nmatch is 0 or REG_NOSUB was specified), to hold the
     input offsets for REG_STARTEND.  Use for output is still entirely con-
     trolled by nmatch; if nmatch is 0 or REG_NOSUB was specified, the value
     of pmatch[0] will not be changed by a successful regexec().

     The regerror() function maps a non-zero errcode from either regcomp() or
     regexec() to a human-readable, printable message.  If preg is non-NULL,
     the error code should have arisen from use of the regex_t pointed to by
     preg, and if the error code came from regcomp(), it should have been the
     result from the most recent regcomp() using that regex_t.  The
     (regerror() may be able to supply a more detailed message using informa-
     tion from the regex_t.)  The regerror() function places the NUL-termi-
     nated message into the buffer pointed to by errbuf, limiting the length
     (including the NUL) to at most errbuf_size bytes.  If the whole message
     will not fit, as much of it as will fit before the terminating NUL is
     supplied.  In any case, the returned value is the size of buffer needed
     to hold the whole message (including terminating NUL).  If errbuf_size is
     0, errbuf is ignored but the return value is still correct.

     If the errcode given to regerror() is first ORed with REG_ITOA, the
     ``message'' that results is the printable name of the error code, e.g.
     ``REG_NOMATCH'', rather than an explanation thereof.  If errcode is
     REG_ATOI, then preg shall be non-NULL and the re_endp member of the
     structure it points to must point to the printable name of an error code;
     in this case, the result in errbuf is the decimal digits of the numeric
     value of the error code (0 if the name is not recognized).  REG_ITOA and
     REG_ATOI are intended primarily as debugging facilities; they are exten-
     sions, compatible with but not specified by IEEE Std 1003.2
     (``POSIX.2''), and should be used with caution in software intended to be
     portable to other systems.  Be warned also that they are considered
     experimental and changes are possible.

     The regfree() function frees any dynamically-allocated storage associated
     with the compiled RE pointed to by preg.  The remaining regex_t is no
     longer a valid compiled RE and the effect of supplying it to regexec() or
     regerror() is undefined.

     None of these functions references global variables except for tables of
     constants; all are safe for use from multiple threads if the arguments
     are safe.


EXTENDED APIS

     These extended APIs are available in Mac OS X 10.8 and beyond, when the
     deployment target is 10.8 or later.  It should also be noted that any of
     the regcomp() variants may be used to initialize a regex_t structure,
     that can then be passed to any of the regexec() variants.  So it is quite
     legal to compile a wide character RE and use it to match a multibyte
     character string, or vice versa.

     The regncomp() routine compiles regular expressions like regcomp(), but
     the length of the regular expression string is specified, allowing a
     string that is not NUL terminated and/or contains NUL characters.  This
     is a modern replacement for using regcomp() with the REG_PEND option.

     Similarly, the regnexec() routine is like regexec(), but the length of
     the string to match is specified, allowing a string that is not NUL ter-
     minated and/or contains NUL characters.

     The regwcomp() and regwexec() variants take a wide-character (wchar_t)
     string for the regular expression and string to match.  And regwncomp()
     and regwnexec() are variants that allow specifying the wide character
     string length, and so allows wide character strings that are not NUL ter-
     minated and/or contains NUL characters.


INTERACTION WITH THE LOCALE

     When regcomp() or one of its variants is run, the regular expression is
     compiled into an internal form, which may include specific information
     about the locale currently in effect, such as equivalence classes or
     multi-character collation symbols.  So a reference to the current locale
     is also stored with the internal form, so that when regexec() is run, it
     can use the same locale (even if the locale is changed in-between the
     calls to regcomp() and regexec()).

     To provide more direct control over which locale is used, routines with
     ``_l'' appended to their names are provided that work just like the vari-
     ants without the ``_l'', except that a locale (via a locale_t variable
     type) is specified directly.  Note that only variants of regcomp() have
     ``_l'' variants, since the regexec() variants just use the reference to
     the locale stored in the internal form.


IMPLEMENTATION CHOICES

     The regex implementation in Mac OS X 10.8 and later is based on a heavily
     modified subset of TRE (http://laurikari.net/tre/).  This provides
     improved performance, better conformance and additional features.  How-
     ever, both API and binary compatibility have been maintained with previ-
     ous releases, so binaries built on previous releases should work on 10.8
     and later, and binaries built on 10.8 and later should be able to run on
     previous releases (as long as none of the new variants or new features
     are used.

     There are a number of decisions that IEEE Std 1003.2 (``POSIX.2'') leaves
     up to the implementor, either by explicitly saying ``undefined'' or by
     virtue of them being forbidden by the RE grammar.  This implementation
     treats them as follows.

     See re_format(7) for a discussion of the definition of case-independent
     matching.

     There is no particular limit on the length of REs, except insofar as mem-
     ory is limited.  Memory usage is approximately linear in RE size, and
     largely insensitive to RE complexity, except for bounded repetitions.
     See BUGS for one short RE using them that will run almost any system out
     of memory.

     A backslashed character other than one specifically given a magic meaning
     by IEEE Std 1003.2 (``POSIX.2'') (such magic meanings occur only in obso-
     lete [``basic''] REs) is taken as an ordinary character.

     Any unmatched `[' is a REG_EBRACK error.

     Equivalence classes cannot begin or end bracket-expression ranges.  The
     endpoint of one range cannot begin another.

     RE_DUP_MAX, the limit on repetition counts in bounded repetitions, is
     255.

     A repetition operator (`?', `*', `+', or bounds) cannot follow another
     repetition operator, except for the use of `?' for minimal repetition
     (for enhanced extended REs; see re_format(7) for details).  A repetition
     operator cannot begin an expression or subexpression or follow `^' or
     `|'.

     `|' cannot appear first or last in a (sub)expression or after another
     `|', i.e., an operand of `|' cannot be an empty subexpression.  An empty
     parenthesized subexpression, `()', is legal and matches an empty
     (sub)string.  An empty string is not a legal RE.

     A `{' followed by a digit is considered the beginning of bounds for a
     bounded repetition, which must then follow the syntax for bounds.  A `{'
     not followed by a digit is considered an ordinary character.

     `^' and `$' beginning and ending subexpressions in obsolete (``basic'')
     REs are anchors, not ordinary characters.


DIAGNOSTICS

     Non-zero error codes from regcomp() and regexec() include the following:

     REG_NOMATCH   The regexec() function failed to match
     REG_BADPAT    invalid regular expression
     REG_ECOLLATE  invalid collating element
     REG_ECTYPE    invalid character class
     REG_EESCAPE   `\' applied to unescapable character
     REG_ESUBREG   invalid backreference number
     REG_EBRACK    brackets `[ ]' not balanced
     REG_EPAREN    parentheses `( )' not balanced
     REG_EBRACE    braces `{ }' not balanced
     REG_BADBR     invalid repetition count(s) in `{ }'
     REG_ERANGE    invalid character range in `[ ]'
     REG_ESPACE    ran out of memory
     REG_BADRPT    `?', `*', or `+' operand invalid
     REG_EMPTY     empty (sub)expression
     REG_ASSERT    cannot happen - you found a bug
     REG_INVARG    invalid argument, e.g. negative-length string
     REG_ILLSEQ    illegal byte sequence (bad multibyte character)


SEE ALSO

     grep(1), re_format(7)

     IEEE Std 1003.2 (``POSIX.2''), sections 2.8 (Regular Expression Notation)
     and B.5 (C Binding for Regular Expression Matching).


HISTORY

     The regex implementation is based on a heavily modified subset of TRE
     (http://laurikari.net/tre/), originally written by Ville Laurikari.  Pre-
     vious releases used an implementation originally written by Henry
     Spencer, and altered for inclusion in the 4.4BSD distribution.


BUGS

     The beginning-of-line and end-of-line anchors ( ``^'' and ``$'') are cur-
     rently implemented so that repetitions can not be applied to them.  The
     standards are unclear about whether this is legal, but other regex pack-
     ages do support this case.  It is best to avoid this non-portable (and
     not really very useful) case.

     The back-reference code is subtle and doubts linger about its correctness
     in complex cases.

     The regexec() variants use one of two internal matching engines.  The
     normal one is linear worst-case time in the length of the text being
     searched, and quadratic worst-case time in the length of the used regular
     expression.  When back-references are used, a slower, backtracking engine
     is used.  While all backtracking matching engines suffer from extreme
     slowness for certain pathological cases, the normal engines doesn't suf-
     fer from these cases.  It is advised to avoid back-references whenever
     possible.

     The regcomp() variants implements bounded repetitions by macro expansion,
     which is costly in time and space if counts are large or bounded repeti-
     tions are nested.  An RE like, say,
     `((((a{1,100}){1,100}){1,100}){1,100}){1,100}' will (eventually) run
     almost any existing machine out of swap space.

     Due to a mistake in IEEE Std 1003.2 (``POSIX.2''), things like `a)b' are
     legal REs because `)' is a special character only in the presence of a
     previous unmatched `('.  This cannot be fixed until the spec is fixed.

     The standard's definition of back references is vague.  For example, does
     `a\(\(b\)*\2\)*d' match `abbbd'?  Until the standard is clarified, behav-
     ior in such cases should not be relied on.

BSD                              Sept 29, 2011                             BSD

Mac OS X 10.8 - Generated Thu Aug 30 11:31:29 CDT 2012