REGCMP(3X) INTERACTIVE UNIX System REGCMP(3X)
NAME
regcmp, regex - compile and execute regular expression
SYNOPSIS
char *regcmp (string1 [, string2, ...], (char *)0)
char *string1, *string2, ...;
char *regex (re, subject[, ret0, ...])
char *re, *subject, *ret0, ...;
extern char *__loc1;
DESCRIPTION
The regcmp function compiles a regular expression (consist-
ing 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 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. 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 their associated mean-
ings.
[]*.^ These symbols retain their meaning in ed(1).
$ Matches the end of the string; \n matches a new-
line.
- 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.
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REGCMP(3X) INTERACTIVE UNIX System REGCMP(3X)
If only m is present (e.g., {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 (*) opera-
tions are equivalent to {1,} and {0,} respec-
tively.
( ... )$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 uncondition-
ally.
( ... ) Parentheses are used for grouping. An operator,
e.g., *, +, {}, 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.
EXAMPLES
Example 1:
char *cursor, *newcursor, *ptr;
...
newcursor = regex((ptr = regcmp("^\n", (char *)0)), cursor);
free(ptr);
This example will match a leading new-line in the subject
string pointed at by cursor.
Example 2:
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);
This example will match through the string ``Testing3'' and
will return the address of the character after the last
matched character (the ``4''). The string ``Testing3'' will
be copied to the character array ret0.
Example 3:
#include "file.i"
char *string, *newcursor;
...
newcursor = regex(name, string);
This example applies a precompiled regular expression in
file.i [see regcmp(1)] against string.
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REGCMP(3X) INTERACTIVE UNIX System REGCMP(3X)
SEE ALSO
regcmp(1), malloc(3C), regexp(5).
ed(1) in the INTERACTIVE UNIX System User's/System
Administrator's Reference Manual.
BUGS
The user program may run out of memory if regcmp is called
iteratively without freeing the vectors no longer required.
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