regcomp(3)                                                   regcomp(3)

  regcomp()

  NAME

    regcomp(), wcs_regcomp(), regexec(), wcs_regexec(), regerror(), regfree()
    - regular-expression library

  SYNOPSIS

    #include 
    #include 

    int regcomp (regex_t *preg, const char *pattern, int cflags);
    int wcs_regcomp (regex_t *preg, const wchar_t *pattern, int cflags);
    int regexec (const regex_t *preg, const char *string,
                 size_t nmatch, regmatch_t pmatch[], int eflags);
    int wcs_regexec (const regex_t *preg, const wchar_t *string,
                 size_t nmatch, regmatch_t pmatch[], int eflags);
    size_t regerror (int errcode, const regex_t *preg,
                    char *errbuf, size_t errbuf_size);
    void regfree(regex_t *preg);

  DESCRIPTION

    The regcomp(3) and wcs_regcomp(3) functions are identical, as are the
    regexec(3) and wcs_regexec(3) functions, except that the wcs_regcomp(3)
    and wcs_regexec(3) functions accept wide characters in the pattern and
    string arguments, respectively.

    These routines implement POSIX 1003.2 regular expressions (REs); see
    re_format(5). The regcomp(3) function compiles an RE written as a string
    into an internal form, regexec(3) or wcs_regexec(3) matches that internal
    form against a string and reports results, regerror(3) transforms error
    codes from either into human-readable messages, and regfree(3) frees any
    dynamically-allocated storage used by the internal form of an RE.

    The header  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(3) or wcs_regcomp(3) 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. Cflags 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, compatible with but not specified by
        POSIX 1003.2, 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(3) or wcs_regcomp(3).

    REG_ICASE
        Compile for matching that ignores upper/lower case distinctions. See
        re_format

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

    REG_NEWLINE
        Compile for newline-sensitive matching. By default, newline 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
        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 POSIX
        1003.2, and should be used with caution in software intended to be
        portable to other systems.

  RETURN VALUES

    When successful, regcomp(3) or wcs_regcomp(3) returns 0 and fills in the
    structure pointed to by preg. One member of that structure (other than
    re_endp is publicized: 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(3) or
    wcs_regcomp(3) fails, it returns a non-zero error code; see ERRORS.

    The regexec(3) or wcs_regexec(3) 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(3) or wcs_regcomp(3).
    The compiled form is not altered during execution of regexec(3) or
    wcs_regexec(3), so a single compiled RE can be used simultaneously 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 POSIX 1003.2, 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 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(3) or wcs_regexec(3) 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 ERRORS.

    If REG_NOSUB was specified in the compilation of the RE, or if nmatch is
    0, regexec(3) or wcs_regexec(3) 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
    respectively 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(3) or
    wcs_regexec(3). An empty substring is denoted by equal offsets, both
    indicating the character following the empty substring.

    The 0th member of the pmatch array is filled in to indicate what substring
    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 controlled by
    nmatch; if nmatch is 0 or REG_NOSUB was specified, the value of pmatch[0
    will not be changed by a successful regexec(3) or wcs_regexec(3).

    regerror(3) maps a non-zero errcode from regcomp(3), wcs_regcomp(3),
    regexec(3), or wcs_regexec(3) 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(3) or
    wcs_regcomp(3), it should have been the result from the most recent
    regcomp(3) or wcs_regcomp(3) using that regex_t. (regerror(3) may be able
    to supply a more detailed message using information from the regex_t.)
    regerror(3) places the NUL-terminated message into the buffer pointed to
    by errbuf limiting the length (including the NUL) to at most errbuf_size
    bytes. If the whole message won't 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(3) 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 extensions,
    compatible with but not specified by POSIX 1003.2, 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.

    regfree(3) 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(3), wcs_regexec(3),
    or regerror(3) 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.

  IMPLEMENTATION CHOICES

    There are a number of decisions that 1003.2 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 for a discussion of the definition of case-independent
    matching.

    There is no particular limit on the length of REs, except insofar as
    memory 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 1003.2 (such magic meanings occur only in obsolete [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. 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.

  NOTE

    This implementation is based on the work of Henry Spencer.

  ERRORS

    Non-zero error codes from regcomp(3), wcs_regcomp(3), regexec(3), and
    wcs_regexec(3) include the following:

    REG_NOMATCH
        regexec(3) or wcs_regexec(3) failed to match

    REG_BADPAT
        invalid regular expression

    REG_ECOLLATE
        invalid collating element

    REG_ECTYPE
        invalid character class

    REG_EESCAPE
        backslash (\) 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
        can't happen--you found a bug

    REG_INVARG
        invalid argument, e.g. negative-length string

  SEE ALSO

    grep(1)

    re_format(5)

  USAGE NOTES

    All of these functions are thread safe.

    None of these functions are async-signal safe.