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diff --git a/regex/regex.3 b/regex/regex.3 new file mode 100644 index 0000000..bc74709 --- /dev/null +++ b/regex/regex.3 @@ -0,0 +1,509 @@ +.TH REGEX 3 "25 Sept 1997" +.BY "Henry Spencer" +.de ZR +.\" one other place knows this name: the SEE ALSO section +.IR regex (7) \\$1 +.. +.SH NAME +regcomp, regexec, regerror, regfree \- regular-expression library +.SH SYNOPSIS +.ft B +.\".na +#include <sys/types.h> +.br +#include <regex.h> +.HP 10 +int regcomp(regex_t\ *preg, const\ char\ *pattern, int\ cflags); +.HP +int\ regexec(const\ regex_t\ *preg, const\ char\ *string, +size_t\ nmatch, regmatch_t\ pmatch[], int\ eflags); +.HP +size_t\ regerror(int\ errcode, const\ regex_t\ *preg, +char\ *errbuf, size_t\ errbuf_size); +.HP +void\ regfree(regex_t\ *preg); +.\".ad +.ft +.SH DESCRIPTION +These routines implement POSIX 1003.2 regular expressions (``RE''s); +see +.ZR . +.I Regcomp +compiles an RE written as a string into an internal form, +.I regexec +matches that internal form against a string and reports results, +.I regerror +transforms error codes from either into human-readable messages, +and +.I regfree +frees any dynamically-allocated storage used by the internal form +of an RE. +.PP +The header +.I <regex.h> +declares two structure types, +.I regex_t +and +.IR regmatch_t , +the former for compiled internal forms and the latter for match reporting. +It also declares the four functions, +a type +.IR regoff_t , +and a number of constants with names starting with ``REG_''. +.PP +.I Regcomp +compiles the regular expression contained in the +.I pattern +string, +subject to the flags in +.IR cflags , +and places the results in the +.I regex_t +structure pointed to by +.IR preg . +.I Cflags +is the bitwise OR of zero or more of the following flags: +.IP REG_EXTENDED \w'REG_EXTENDED'u+2n +Compile modern (``extended'') REs, +rather than the obsolete (``basic'') REs that +are the default. +.IP REG_BASIC +This is a synonym for 0, +provided as a counterpart to REG_EXTENDED to improve readability. +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. +.IP 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 +.IR regcomp . +.IP REG_ICASE +Compile for matching that ignores upper/lower case distinctions. +See +.ZR . +.IP REG_NOSUB +Compile for matching that need only report success or failure, +not what was matched. +.IP 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. +.IP REG_PEND +The regular expression ends, +not at the first NUL, +but just before the character pointed to by the +.I re_endp +member of the structure pointed to by +.IR preg . +The +.I re_endp +member is of type +.IR 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. +.PP +When successful, +.I regcomp +returns 0 and fills in the structure pointed to by +.IR preg . +One member of that structure +(other than +.IR re_endp ) +is publicized: +.IR re_nsub , +of type +.IR 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 +.I regcomp +fails, it returns a non-zero error code; +see DIAGNOSTICS. +.PP +.I Regexec +matches the compiled RE pointed to by +.I preg +against the +.IR string , +subject to the flags in +.IR eflags , +and reports results using +.IR nmatch , +.IR pmatch , +and the returned value. +The RE must have been compiled by a previous invocation of +.IR regcomp . +The compiled form is not altered during execution of +.IR regexec , +so a single compiled RE can be used simultaneously by multiple threads. +.PP +By default, +the NUL-terminated string pointed to by +.I string +is considered to be the text of an entire line, +with the NUL indicating the end of the line. +(That is, +any other end-of-line marker is considered to have been removed +and replaced by the NUL.) +The +.I eflags +argument is the bitwise OR of zero or more of the following flags: +.IP REG_NOTBOL \w'REG_STARTEND'u+2n +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. +.IP 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. +.IP REG_STARTEND +The string is considered to start at +\fIstring\fR\ + \fIpmatch\fR[0].\fIrm_so\fR +and to have a terminating NUL located at +\fIstring\fR\ + \fIpmatch\fR[0].\fIrm_eo\fR +(there need not actually be a NUL at that location), +regardless of the value of +.IR nmatch . +See below for the definition of +.IR pmatch +and +.IR 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 \fIrm_so\fR does not imply REG_NOTBOL; +REG_STARTEND affects only the location of the string, +not how it is matched. +.PP +See +.ZR +for a discussion of what is matched in situations where an RE or a +portion thereof could match any of several substrings of +.IR string . +.PP +Normally, +.I 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. +.PP +If REG_NOSUB was specified in the compilation of the RE, +or if +.I nmatch +is 0, +.I regexec +ignores the +.I pmatch +argument (but see below for the case where REG_STARTEND is specified). +Otherwise, +.I pmatch +points to an array of +.I nmatch +structures of type +.IR regmatch_t . +Such a structure has at least the members +.I rm_so +and +.IR rm_eo , +both of type +.I regoff_t +(a signed arithmetic type at least as large as an +.I off_t +and a +.IR 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 +.I string +argument given to +.IR regexec . +An empty substring is denoted by equal offsets, +both indicating the character following the empty substring. +.PP +The 0th member of the +.I pmatch +array is filled in to indicate what substring of +.I string +was matched by the entire RE. +Remaining members report what substring was matched by parenthesized +subexpressions within the RE; +member +.I i +reports subexpression +.IR 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\(emcorresponding either to subexpressions that +did not participate in the match at all, or to subexpressions that do not +exist in the RE (that is, \fIi\fR\ > \fIpreg\fR\->\fIre_nsub\fR)\(emhave both +.I rm_so +and +.I 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 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.) +.PP +If REG_STARTEND is specified, +.I pmatch +must point to at least one +.I regmatch_t +(even if +.I nmatch +is 0 or REG_NOSUB was specified), +to hold the input offsets for REG_STARTEND. +Use for output is still entirely controlled by +.IR nmatch ; +if +.I nmatch +is 0 or REG_NOSUB was specified, +the value of +.IR pmatch [0] +will not be changed by a successful +.IR regexec . +.PP +.I Regerror +maps a non-zero +.I errcode +from either +.I regcomp +or +.I regexec +to a human-readable, printable message. +If +.I preg +is non-NULL, +the error code should have arisen from use of +the +.I regex_t +pointed to by +.IR preg , +and if the error code came from +.IR regcomp , +it should have been the result from the most recent +.I regcomp +using that +.IR regex_t . +.RI ( Regerror +may be able to supply a more detailed message using information +from the +.IR regex_t .) +.I Regerror +places the NUL-terminated message into the buffer pointed to by +.IR errbuf , +limiting the length (including the NUL) to at most +.I 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 +.I errbuf_size +is 0, +.I errbuf +is ignored but the return value is still correct. +.PP +If the +.I errcode +given to +.I 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 +.I errcode +is REG_ATOI, +then +.I preg +shall be non-NULL and the +.I 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 +.I 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. +.PP +.I Regfree +frees any dynamically-allocated storage associated with the compiled RE +pointed to by +.IR preg . +The remaining +.I regex_t +is no longer a valid compiled RE +and the effect of supplying it to +.I regexec +or +.I regerror +is undefined. +.PP +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. +.SH 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. +.PP +See +.ZR +for a discussion of the definition of case-independent matching. +.PP +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. +.PP +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. +.PP +Any unmatched [ is a REG_EBRACK error. +.PP +Equivalence classes cannot begin or end bracket-expression ranges. +The endpoint of one range cannot begin another. +.PP +RE_DUP_MAX, the limit on repetition counts in bounded repetitions, is 255. +.PP +A repetition operator (?, *, +, or bounds) cannot follow another +repetition operator. +A repetition operator cannot begin an expression or subexpression +or follow `^' or `|'. +.PP +`|' 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. +.PP +A `{' followed by a digit is considered the beginning of bounds for a +bounded repetition, which must then follow the syntax for bounds. +A `{' \fInot\fR followed by a digit is considered an ordinary character. +.PP +`^' and `$' beginning and ending subexpressions in obsolete (``basic'') +REs are anchors, not ordinary characters. +.SH SEE ALSO +grep(1), regex(7) +.PP +POSIX 1003.2, sections 2.8 (Regular Expression Notation) +and +B.5 (C Binding for Regular Expression Matching). +.SH DIAGNOSTICS +Non-zero error codes from +.I regcomp +and +.I regexec +include the following: +.PP +.nf +.ta \w'REG_ECOLLATE'u+3n +REG_NOMATCH regexec() failed to match +REG_BADPAT invalid regular expression +REG_ECOLLATE invalid collating element +REG_ECTYPE invalid character class +REG_EESCAPE \e 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''\(emyou found a bug +REG_INVARG invalid argument, e.g. negative-length string +.fi +.SH HISTORY +Written by Henry Spencer, +henry@zoo.toronto.edu. +.SH BUGS +This is an alpha release with known defects. +Please report problems. +.PP +There is one known functionality bug. +The implementation of internationalization is incomplete: +the locale is always assumed to be the default one of 1003.2, +and only the collating elements etc. of that locale are available. +.PP +The back-reference code is subtle and doubts linger about its correctness +in complex cases. +.PP +.I Regexec +performance is poor. +This will improve with later releases. +.I Nmatch +exceeding 0 is expensive; +.I nmatch +exceeding 1 is worse. +.I Regexec +is largely insensitive to RE complexity \fIexcept\fR 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. +.PP +.I Regcomp +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. +.PP +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. +.PP +Due to a mistake in 1003.2, things like `a)b' are legal REs because `)' is +a special character only in the presence of a previous unmatched `('. +This can't be fixed until the spec is fixed. +.PP +The standard's definition of back references is vague. +For example, does +`a\e(\e(b\e)*\e2\e)*d' match `abbbd'? +Until the standard is clarified, +behavior in such cases should not be relied on. +.PP +The implementation of word-boundary matching is a bit of a kludge, +and bugs may lurk in combinations of word-boundary matching and anchoring. |