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

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 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 list shows the valid symbols and their associated meanings.

[ ] ∗ . ^ These symbols retain their meaning from 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.  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 (∗) operations are equivalent to {1,} and {0,} respectively. 

( . . . )$n
The value of the enclosed regular expression is to be returned. The value is 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 matches 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 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.

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.

These routines are kept in /lib/libPW.a. 

SEE ALSO

ed(1), malloc(3C), regcmp(1)

BUGS

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

September 02, 1992