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.TH REGEXP 2

.SH NAME

regcomp, regcomplit, regcompnl, regexec, regsub, rregexec, rregsub, regerror \- regular expression

.SH SYNOPSIS

.B #include <u.h>

.br

.B #include <libc.h>

.br

.B #include <regexp.h>

.PP

.ta \w'\fLRegprog 'u

.B

Reprog	*regcomp(char *exp)

.PP

.B

Reprog	*regcomplit(char *exp)

.PP

.B

Reprog	*regcompnl(char *exp)

.PP

.nf

.B

int  regexec(Reprog *prog, char *string, Resub *match, int msize)

.PP

.nf

.B

void regsub(char *source, char *dest, int dlen, Resub *match, int msize)

.PP

.nf

.B

int  rregexec(Reprog *prog, Rune *string, Resub *match, int msize)

.PP

.nf

.B

void rregsub(Rune *source, Rune *dest, int dlen, Resub *match, int msize)

.PP

.B

void regerror(char *msg)

.SH DESCRIPTION

.I Regcomp

compiles a

regular expression and returns

a pointer to the generated description.

The space is allocated by

.IR malloc (2)

and may be released by

.IR free .

Regular expressions are exactly as in

.IR regexp (6).

.PP

.I Regcomplit

is like

.I regcomp

except that all characters are treated literally.

.I Regcompnl

is like

.I regcomp

except that the

.B .

metacharacter matches all characters, including newlines.

.PP

.I Regexec

matches a null-terminated

.I string

against the compiled regular expression in

.IR prog .

If it matches,

.I regexec

returns

.B 1

and fills in the array

.I match

with character pointers to the substrings of

.I string

that correspond to the

parenthesized subexpressions of 

.IR exp :

.BI match[ i ].sp

points to the beginning and

.BI match[ i ].ep

points just beyond

the end of the

.IR i th

substring.

(Subexpression

.I i

begins at the

.IR i th

left parenthesis, counting from 1.)

Pointers in

.B match[0]

pick out the substring that corresponds to

the whole regular expression.

Unused elements of

.I match

are filled with zeros.

Matches involving

.LR * ,

.LR + ,

and 

.L ?

are extended as far as possible.

The number of array elements in 

.I match

is given by

.IR msize .

The structure of elements of

.I match 

is:

.IP

.EX

typedef struct {

	union {

	   char *sp;

	   Rune *rsp;

	};

	union {

	   char *ep;

	   Rune *rep;

	};

} Resub;

.EE

.LP

If

.B match[0].sp

is nonzero on entry,

.I regexec

starts matching at that point within

.IR string .

If

.B match[0].ep

is nonzero on entry,

the last character matched is the one

preceding that point.

.PP

.I Regsub

places in

.I dest

a substitution instance of

.I source

in the context of the last

.I regexec

performed using

.IR match .

Each instance of

.BI \e n\f1,

where

.I n

is a digit, is replaced by the

string delimited by

.BI match[ n ].sp

and

.BI match[ n ].ep\f1.

Each instance of 

.L &

is replaced by the string delimited by

.B match[0].sp

and

.BR match[0].ep .

The substitution will always be null terminated and

trimmed to fit into dlen bytes.

.PP

.IR Regerror ,

called whenever an error is detected in

.IR regcomp ,

writes the string

.I msg

on the standard error file and exits.

.I Regerror

can be replaced to perform

special error processing.

If the user supplied

.I regerror

returns rather than exits,

.I regcomp

will return 0. 

.PP

.I Rregexec

and

.I rregsub

are variants of 

.I regexec

and

.I regsub

that use strings of

.B Runes

instead of strings of

.BR chars .

With these routines, the 

.I rsp

and

.I rep

fields of the

.I match

array elements should be used.

.SH SOURCE

.B /sys/src/libregexp

.SH "SEE ALSO"

.IR grep (1)

.SH DIAGNOSTICS

.I Regcomp

returns 

.B 0

for an illegal expression

or other failure.

.I Regexec

returns 0

if

.I string

is not matched.

.SH BUGS

There is no way to specify or match a NUL character; NULs terminate patterns and strings.