regcmp(3G)regcmp(3G)NAME
regcmp, regex - compile and execute regular expression
SYNOPSIS
#include <libgen.h>
cc [flag ...] file ... -lgen [library ...]
char *regcmp (const char *string1 [, char *string2, ...],
(char *)0);
char *regex (const char *re, const char *subject
[, char *ret0, ...]);
extern char *__loc1;
DESCRIPTION
regcmp compiles a regular expression (consisting of the concatenated
arguments) and returns a pointer to the compiled form. malloc(3C) 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 time.
regex executes a compiled pattern against the subject string. Additional
arguments are passed to receive values back. regex 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. Note
that in the subject string the newline character (\n) is not considered a
delimiter, thus constructs such as anchoring work only on the basis of
the entire string, not any individual 'lines' within the string. regcmp
and regex 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 meanings.
[]*.^ These symbols retain their meaning in ed(1).
$ Matches the end of the string; \n matches a newline.
- Within brackets the minus means through. For example, [a-z] is
equivalent to [abcd...xyz]. 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 [0-9][0-9]*.
{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
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regcmp(3G)regcmp(3G)
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. regex 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. In
some cases (parenthesis () and braces {}) this is exactly the opposite of
ed(1).
EXAMPLES
The following example matches a leading newline in the subject string
pointed at by cursor.
char *cursor, *newcursor, *ptr;
...
newcursor = regex((ptr = (char *)regcmp("^\n", (char *)0)), cursor);
free(ptr);
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 ALSOed(1), regcmp(1), malloc(3C)
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The user program may run out of memory if regcmp is called iteratively
without freeing the vectors no longer required.
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