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regex (3)
  • regex (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • >> regex (3) ( FreeBSD man: Библиотечные вызовы )
  • regex (3) ( Русские man: Библиотечные вызовы )
  • regex (3) ( Linux man: Библиотечные вызовы )
  • regex (5) ( Solaris man: Форматы файлов )
  • regex (7) ( Русские man: Макропакеты и соглашения )
  • regex (7) ( Linux man: Макропакеты и соглашения )
  • Ключ regex обнаружен в базе ключевых слов.

  • BSD mandoc
     

    NAME

    
    
    regcomp
    
     
    regexec
    
     
    regerror
    
     
    regfree
    
     - regular-expression library
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <regex.h>
    int Fo regcomp Fa regex_t * restrict preg const char * restrict pattern int cflags Fc Ft int Fo regexec Fa const regex_t * restrict preg const char * restrict string Fa size_t nmatch regmatch_t pmatch[restrict] int eflags Fc Ft size_t Fo regerror Fa int errcode const regex_t * restrict preg Fa char * restrict errbuf size_t errbuf_size Fc Ft void regfree (regex_t *preg);
     

    DESCRIPTION

    These routines implement St -p1003.2 regular expressions (Do RE Dc s ) see re_format7. 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 ();
    transforms error codes from either into human-readable messages, and regfree ();
    frees any dynamically-allocated storage used by the internal form of an RE.

    The header    #include <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 Fa pattern string, subject to the flags in Fa cflags , and places the results in the regex_t structure pointed to by Fa preg . The Fa 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, compatible with but not specified by St -p1003.2 , 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_ICASE
    Compile for matching that ignores upper/lower case distinctions. See re_format7.
    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 Fa 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 St -p1003.2 , and should be used with caution in software intended to be portable to other systems.

    When successful, regcomp ();
    returns 0 and fills in the structure pointed to by Fa 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 ();
    fails, it returns a non-zero error code; see Sx DIAGNOSTICS .

    The regexec ();
    function matches the compiled RE pointed to by Fa preg against the Fa string , subject to the flags in Fa eflags , and reports results using Fa nmatch , Fa 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 simultaneously by multiple threads.

    By default, the NUL-terminated string pointed to by Fa string is considered to be the text of an entire line, minus any terminating newline. The Fa 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 Fa string + Fa pmatch Ns [0]. Ns Va rm_so and to have a terminating NUL located at Fa string + Fa pmatch Ns [0]. Ns Va rm_eo (there need not actually be a NUL at that location), regardless of the value of Fa nmatch . See below for the definition of Fa pmatch and Fa nmatch . This is an extension, compatible with but not specified by St -p1003.2 , 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_format7 for a discussion of what is matched in situations where an RE or a portion thereof could match any of several substrings of Fa 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 Sx DIAGNOSTICS .

    If REG_NOSUB was specified in the compilation of the RE, or if Fa nmatch is 0, regexec ();
    ignores the Fa pmatch argument (but see below for the case where REG_STARTEND is specified). Otherwise, Fa pmatch points to an array of Fa 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 Fa string argument given to regexec (.);
    An empty substring is denoted by equal offsets, both indicating the character following the empty substring.

    The 0th member of the Fa pmatch array is filled in to indicate what substring of Fa 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 > Fa preg Ns -> Ns Va 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 So Li b Sc Ns 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, Fa pmatch must point to at least one regmatch_t (even if Fa nmatch is 0 or REG_NOSUB was specified), to hold the input offsets for REG_STARTEND Use for output is still entirely controlled by Fa nmatch ; if Fa nmatch is 0 or REG_NOSUB was specified, the value of Fa pmatch Ns [0] will not be changed by a successful regexec (.);

    The regerror ();
    function maps a non-zero Fa errcode from either regcomp ();
    or regexec ();
    to a human-readable, printable message. If Fa preg is non- NULL the error code should have arisen from use of the regex_t pointed to by Fa 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 Fn ( regerror may be able to supply a more detailed message using information from the regex_t . ) The regerror ();
    function places the NUL-terminated message into the buffer pointed to by Fa errbuf , limiting the length (including the NUL) to at most Fa 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 Fa errbuf_size is 0, Fa errbuf is ignored but the return value is still correct.

    If the Fa 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 Fa errcode is REG_ATOI then Fa 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 Fa 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 St -p1003.2 , 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 Fa 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.  

    IMPLEMENTATION CHOICES

    There are a number of decisions that St -p1003.2 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_format7 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 Sx 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 St -p1003.2 (such magic meanings occur only in obsolete Bq Dq 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.  

    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_format7

    St -p1003.2 , sections 2.8 (Regular Expression Notation) and B.5 (C Binding for Regular Expression Matching).  

    HISTORY

    Originally written by An Henry Spencer . Altered for inclusion in the BSD 4.4 distribution.  

    BUGS

    This is an alpha release with known defects. Please report problems.

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

    The regexec ();
    function performance is poor. This will improve with later releases. The Fa nmatch argument exceeding 0 is expensive; Fa nmatch exceeding 1 is worse. The regexec ();
    function is largely insensitive to RE complexity except that back references are massively expensive. RE length does matter; in particular, there is a strong speed bonus for keeping RE length under about 30 characters, with most special characters counting roughly double.

    The regcomp ();
    function implements bounded repetitions by macro expansion, which is costly in time and space if counts are large or bounded repetitions 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.

    There are suspected problems with response to obscure error conditions. Notably, certain kinds of internal overflow, produced only by truly enormous REs or by multiply nested bounded repetitions, are probably not handled well.

    Due to a mistake in St -p1003.2 , 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, behavior in such cases should not be relied on.

    The implementation of word-boundary matching is a bit of a kludge, and bugs may lurk in combinations of word-boundary matching and anchoring.

    Word-boundary matching does not work properly in multibyte locales.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    IMPLEMENTATION CHOICES
    DIAGNOSTICS
    SEE ALSO
    HISTORY
    BUGS


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