REGCMP(S) UNIX System V REGCMP(S)
Name
regcmp, regex - compile and execute regular expression
Syntax
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
(consisting of the concatenated arguments) and returns a
pointer to the compiled form. The malloc(S) 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(CP) 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(C); however,
the syntax and semantics have been changed slightly. The
following are the valid symbols and their associated
meanings.
[]*.^ These symbols retain their meaning in ed(C).
$ 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.
If only m is present (for example, {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. regex makes its assignments
unconditionally.
( ... ) 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(CP)) against string.
See Also
regcmp(CP), malloc(S), ed(C)
Notes
The user program may run out of memory if regcmp is called
iteratively without freeing the vectors no longer required.
(printed 6/20/89)