regcmp(3x)
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;
cc files... -1PW
DESCRIPTION
The regcmp subroutine compiles a regular expression and returns a pointer to the compiled form. To create space for the vector, malloc(3) is used. It is the user’s responsibility to free unneeded space so allocated. A NULL return from regcmp indicates an incorrect argument. The regcmp(1) command has been written to generally preclude the need for this routine at execution time.
The regex subroutine executes a compiled pattern against the subject string. Additional arguments are passed to receive values back. The regex subroutine 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. Both 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 meanings.
[]*.^ These symbols retain their current meaning.
$ 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. The regex subroutine 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 to be used as themselves.
EXAMPLES
Example 1:
char ∗cursor, ∗newcursor, ∗ptr;
...
newcursor = regex((ptr = regcmp("^\n", 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", 0);
newcursor = regex(name, "123Testing321", ret0);
This example will match through the string “Testing3” and will return the address of the character after the last matched character (cursor+11). 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 against string. For further information, see regcmp(1).
This routine is kept in /lib/libPW.a.
RESTRICTIONS
The user program may run out of memory if regcmp is called iteratively without freeing the vectors no longer required. The following user-supplied replacement for malloc(3) reuses the same vector saving time and space:
/∗ user’s program ∗/
...
char ∗
malloc(n)
unsigned n;
{
static char rebuf[512];
return (n <= sizeof rebuf) ? rebuf : NULL;
}