REGEXP(2)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, int dlen, Resub *match, int msize)
int rregexec(Reprog *prog, Rune *string, Resub *match, int msize)
void rregsub(Rune *source, Rune *dest, int dlen, 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 parenthesis, 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
\n,
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 delimited by
match[0].sp
and
match[0].ep.
The substitution will always be null terminated and
trimmed to fit into dlen bytes.
Regerror,
called whenever an error is detected in
regcomp,
writes the string
msg
on the standard error file and exits.
Regerror
can be replaced to perform
special error processing.
If the user supplied
regerror
returns rather than exits,
regcomp
will return 0.
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.
The size of a character class and the number of sub-expression matches are hard-coded
limits. The library uses the worst-case space estimate for allocating VM runtime threads.
HISTORY
Regexp(2)
first appeared in Plan 9 from Bell Labs. This implementation was written from
scratch for 9front (May, 2016).