common/man/re.3

        .fp 5 CW
..
.nr ;G \\n(.f
.Af "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7" "\\$8" "\\$9"
\\*(;G
..
.aF 5 \\n(.f "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
..
.aF 5 1 "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
..
.aF 1 5 "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6" "\\$7"
..


 0
..


..
 RE 3
 NAME
recomp, reexec, ressub, refree, reerror - regular expression library
 SYNOPSIS
.EX
#include <re.h>

Re_program_t* recomp(char* pattern, int flags);
int reexec(Re_program_t* re, char* source);
void ressub(Re_program_t* re, Sfio_t* sp, char* old, char* new, int flags);
void reerror(char* message);
void refree(Re_program_t* re);

 DESCRIPTION
.L recomp
compiles a regular expression in
 pattern and returns a pointer to the compiled regular expression.
The space is allocated by
 malloc (3) and may be released by
.LR refree .
Regular expressions are as in
 egrep (1) except that newlines are treated as ordinary
characters and
.L $
matches the end of a null-terminated string.
 flags may be
.L RE_EDSTYLE
which specifies
 ed (1) style special characters,
.LR \e( ,
.LR \e) ,
.LR \e? ,
.L \e+
and
.L \e|
for the
 egrep (1) .LR ( ,
.LR ) ,
.LR ? ,
.L +
and
.LR | ,
respectively.

.L reexec
matches the null-terminated
 source string against the compiled regular expression
 re from a previous call to
.LR recomp .
If it matches,
.L reexec
returns a non-zero value.
If
 flags is
.L RE_MATCH
then the array
 re->match is filled with character pointers to the substrings of
 source that correspond to the
parenthesized subexpressions of
 pattern :  re->match[i].sp points to the beginning and
 re->match[i].ep points just beyond
the end of substring
 i . (Subexpression
 i begins at the
 i th matched left parenthesis, counting from 1.)
Pointers in
 re->match[0] pick out the substring that corresponds to
the entire regular expression.
Unused elements of
 re->match are filled with zeros.
Matches involving
.LR * ,
.LR + ,
and
.L ?
are extended as far as possible.
A maximum of 9 subexpressions will be matched.
The structure of elements of
 re->match  is:
 typedef struct
 {
 char* sp;
 char* ep;
 } rematch;


.L ressub
places in the
 sfio (3) stream
 sp a substitution instance of
 old to
 new in
 source in the context of the last
.L reexec
performed on
 re->match . Each instance of
.LI \e n ,
where
 n is a digit, is replaced by the
string delimited by
.LI re->match[ n ].sp
and
.LI re->match[ n ].ep .
Each instance of
.L &
is replaced by the string delimited by
 re->match[0].sp and
 re->match[0].ep . If
.L RE_ALL
is set in
 flags then all occurrences of
 old are replaced by
 new . If
.L RE_LOWER
.RL [ RE_UPPER ]
is set in
 flags then
 old is converted to lower [upper] case.

.L reerror,
called whenever an error is detected in
.L recomp,
.L reexec,
or
.L ressub,
writes the string
 msg on the standard error file and exits.
.L reerror
may be replaced to perform
special error processing.
 DIAGNOSTICS
.L recomp
returns 0 for an invalid expression or other failure.
.L reexec
returns 1 if
 source is accepted, 0 otherwise.
 "SEE ALSO"
ed(1), grep(1), expr(1)