REGCMP(3C) Standard C Library Functions REGCMP(3C)


regcmp, regex - compile and execute regular expression


#include <libgen.h>

char *regcmp(const char *string1, /* char *string2 */ ...,
int /*(char*)0*/);

char *regex(const char *re, const char *subject,
/* char *ret0 */ ...);

extern char *__loc1;


The regcmp() function compiles a regular expression (consisting of the
concatenated arguments) and returns a pointer to the compiled form. The
malloc(3C) function is used to create space for the compiled form. It is
the user's responsibility to free unneeded space so allocated. A NULL
return from regcmp() indicates an incorrect argument. regcmp(1) has been
written to generally preclude the need for this routine at execution

The regex() function executes a compiled pattern against the subject
string. Additional arguments are passed to receive values back. The
regex() function returns NULL on failure or a pointer to the next
unmatched character on success. A global character pointer __loc1 points
to where the match began. The regcmp() and regex() functions were mostly
borrowed from the editor ed(1); however, the syntax and semantics have
been changed slightly. The following are the valid symbols and associated

This group of symbols retains its meaning as described
on the regexp(7) manual page.

Matches the end of the string; \n matches a newline.

Within brackets the minus means through. For example,
[a-z] is equivalent to []. The - can appear
as itself only if used as the first or last character.
For example, the character class expression []-]
matches the characters ] and -.

A regular expression followed by + means one or more
times. For example, [0-9]+ is equivalent to

{m} {m,} {m,u}
Integer values enclosed in {} indicate the number of
times the preceding regular expression is to be
applied. The value m is the minimum number and u is a
number, less than 256, which is the maximum. If only m
is present (that is, {m}), it indicates the exact
number of times the regular expression is to be
applied. The value {m,} is analogous to {m,infinity}.
The plus (+) and star (*) operations are equivalent to
{1,} and {0,} respectively.

( ... )$n
The value of the enclosed regular expression is to be
returned. The value will be stored in the (n+1)th
argument following the subject argument. At most, ten
enclosed regular expressions are allowed. The regex()
function makes its assignments unconditionally.

( ... )
Parentheses are used for grouping. An operator, for
example, *, +, {}, can work on a single character or a
regular expression enclosed in parentheses. For
example, (a*(cb+)*)$0. By necessity, all the above
defined symbols are special. They must, therefore, be
escaped with a \ (backslash) to be used as themselves.


Example 1: Example matching a leading newline in the subject string.

The following example matches a leading newline in the subject string
pointed at by cursor.

char *cursor, *newcursor, *ptr;
newcursor = regex((ptr = regcmp("^\n", (char *)0)), cursor);

The following example matches through the string Testing3 and returns the
address of the character after the last matched character (the ``4'').
The string Testing3 is copied to the character array ret0.

char ret0[9];
char *newcursor, *name;
name = regcmp("([A-Za-z][A-za-z0-9]{0,7})$0", (char *)0);
newcursor = regex(name, "012Testing345", ret0);

The following example applies a precompiled regular expression in file.i
(see regcmp(1)) against string.

#include "file.i"
char *string, *newcursor;
newcursor = regex(name, string);


See attributes(7) for descriptions of the following attributes:

|MT-Level | MT-Safe |


ed(1), regcmp(1), malloc(3C), attributes(7), regexp(7)


The user program may run out of memory if regcmp() is called iteratively
without freeing the vectors no longer required.

When compiling multithreaded applications, the _REENTRANT flag must be
defined on the compile line. This flag should only be used in
multithreaded applications.

November 14, 2002 REGCMP(3C)