regexp(2) [plan9 man page]
REGEXP(2) System Calls Manual REGEXP(2) NAME
regcomp, regcomplit, regcompnl, regexec, regsub, rregexec, rregsub, regerror - regular expression SYNOPSIS
#include <u.h> #include <libc.h> #include <regexp.h> Reprog *regcomp(char *exp) Reprog *regcomplit(char *exp) Reprog *regcompnl(char *exp) int regexec(Reprog *prog, char *string, Resub *match, int msize) void regsub(char *source, char *dest, Resub *match, int msize) int rregexec(Reprog *prog, Rune *string, Resub *match, int msize) void rregsub(Rune *source, Rune *dest, Resub *match, int msize) void regerror(char *msg) DESCRIPTION
Regcomp compiles a regular expression and returns a pointer to the generated description. The space is allocated by malloc(2) and may be released by free. Regular expressions are exactly as in regexp(6). Regcomplit is like regcomp except that all characters are treated literally. Regcompnl is like regcomp except that the . metacharacter matches all characters, including newlines. Regexec matches a null-terminated string against the compiled regular expression in prog. If it matches, regexec returns 1 and fills in the array match with character pointers to the substrings of string that correspond to the parenthesized subexpressions of exp: match[i].sp points to the beginning and match[i].ep points just beyond the end of the ith substring. (Subexpression i begins at the ith left parenthe- sis, counting from 1.) Pointers in match[0] pick out the substring that corresponds to the whole regular expression. Unused elements of match are filled with zeros. Matches involving and are extended as far as possible. The number of array elements in match is given by msize. The structure of elements of match is: typedef struct { union { char *sp; Rune *rsp; }; union { char *ep; Rune *rep; }; } Resub; If match[0].sp is nonzero on entry, regexec starts matching at that point within string. If match[0].ep is nonzero on entry, the last character matched is the one preceding that point. Regsub places in dest a substitution instance of source in the context of the last regexec performed using match. Each instance of , where n is a digit, is replaced by the string delimited by match[n].sp and match[n].ep. Each instance of is replaced by the string delim- ited by match[0].sp and match[0].ep. Regerror, called whenever an error is detected in regcomp, regexec, or regsub, writes the string msg on the standard error file and exits. Regerror can be replaced to perform special error processing. Rregexec and rregsub are variants of regexec and regsub that use strings of Runes instead of strings of chars. With these routines, the rsp and rep fields of the match array elements should be used. SOURCE
/sys/src/libregexp SEE ALSO
grep(1) DIAGNOSTICS
Regcomp returns 0 for an illegal expression or other failure. Regexec returns 0 if string is not matched. BUGS
There is no way to specify or match a NUL character; NULs terminate patterns and strings. REGEXP(2)
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REGEXP(3) Library Functions Manual REGEXP(3) NAME
regcomp, regexec, regsub, regerror - regular expression handler SYNOPSIS
#include <regexp.h> regexp *regcomp(exp) char *exp; int regexec(prog, string) regexp *prog; char *string; regsub(prog, source, dest) regexp *prog; char *source; char *dest; regerror(msg) char *msg; DESCRIPTION
These functions implement egrep(1)-style regular expressions and supporting facilities. Regcomp compiles a regular expression into a structure of type regexp, and returns a pointer to it. The space has been allocated using malloc(3) and may be released by free. Regexec matches a NUL-terminated string against the compiled regular expression in prog. It returns 1 for success and 0 for failure, and adjusts the contents of prog's startp and endp (see below) accordingly. The members of a regexp structure include at least the following (not necessarily in order): char *startp[NSUBEXP]; char *endp[NSUBEXP]; where NSUBEXP is defined (as 10) in the header file. Once a successful regexec has been done using the regexp, each startp-endp pair describes one substring within the string, with the startp pointing to the first character of the substring and the endp pointing to the first character following the substring. The 0th substring is the substring of string that matched the whole regular expression. The oth- ers are those substrings that matched parenthesized expressions within the regular expression, with parenthesized expressions numbered in left-to-right order of their opening parentheses. Regsub copies source to dest, making substitutions according to the most recent regexec performed using prog. Each instance of `&' in source is replaced by the substring indicated by startp[0] and endp[0]. Each instance of ` ', where n is a digit, is replaced by the sub- string indicated by startp[n] and endp[n]. To get a literal `&' or ` ' into dest, prefix it with `'; to get a literal `' preceding `&' or ` ', prefix it with another `'. Regerror is called whenever an error is detected in regcomp, regexec, or regsub. The default regerror writes the string msg, with a suit- able indicator of origin, on the standard error output and invokes exit(2). Regerror can be replaced by the user if other actions are desirable. REGULAR EXPRESSION SYNTAX
A regular expression is zero or more branches, separated by `|'. It matches anything that matches one of the branches. A branch is zero or more pieces, concatenated. It matches a match for the first, followed by a match for the second, etc. A piece is an atom possibly followed by `*', `+', or `?'. An atom followed by `*' matches a sequence of 0 or more matches of the atom. An atom followed by `+' matches a sequence of 1 or more matches of the atom. An atom followed by `?' matches a match of the atom, or the null string. An atom is a regular expression in parentheses (matching a match for the regular expression), a range (see below), `.' (matching any sin- gle character), `^' (matching the null string at the beginning of the input string), `$' (matching the null string at the end of the input string), a `' followed by a single character (matching that character), or a single character with no other significance (matching that character). A range is a sequence of characters enclosed in `[]'. It normally matches any single character from the sequence. If the sequence begins with `^', it matches any single character not from the rest of the sequence. If two characters in the sequence are separated by `-', this is shorthand for the full list of ASCII characters between them (e.g. `[0-9]' matches any decimal digit). To include a literal `]' in the sequence, make it the first character (following a possible `^'). To include a literal `-', make it the first or last character. AMBIGUITY
If a regular expression could match two different parts of the input string, it will match the one which begins earliest. If both begin in the same place but match different lengths, or match the same length in different ways, life gets messier, as follows. In general, the possibilities in a list of branches are considered in left-to-right order, the possibilities for `*', `+', and `?' are con- sidered longest-first, nested constructs are considered from the outermost in, and concatenated constructs are considered leftmost-first. The match that will be chosen is the one that uses the earliest possibility in the first choice that has to be made. If there is more than one choice, the next will be made in the same manner (earliest possibility) subject to the decision on the first choice. And so forth. For example, `(ab|a)b*c' could match `abc' in one of two ways. The first choice is between `ab' and `a'; since `ab' is earlier, and does lead to a successful overall match, it is chosen. Since the `b' is already spoken for, the `b*' must match its last possibility--the empty string--since it must respect the earlier choice. In the particular case where no `|'s are present and there is only one `*', `+', or `?', the net effect is that the longest possible match will be chosen. So `ab*', presented with `xabbbby', will match `abbbb'. Note that if `ab*' is tried against `xabyabbbz', it will match `ab' just after `x', due to the begins-earliest rule. (In effect, the decision on where to start the match is the first choice to be made, hence subsequent choices must respect it even if this leads them to less-preferred alternatives.) SEE ALSO
egrep(1), expr(1) DIAGNOSTICS
Regcomp returns NULL for a failure (regerror permitting), where failures are syntax errors, exceeding implementation limits, or applying `+' or `*' to a possibly-null operand. HISTORY
Both code and manual page were written at U of T. They are intended to be compatible with the Bell V8 regexp(3), but are not derived from Bell code. BUGS
Empty branches and empty regular expressions are not portable to V8. The restriction against applying `*' or `+' to a possibly-null operand is an artifact of the simplistic implementation. Does not support egrep's newline-separated branches; neither does the V8 regexp(3), though. Due to emphasis on compactness and simplicity, it's not strikingly fast. It does give special attention to handling simple cases quickly. 2 April 1986 REGEXP(3)