NAME

regex, regcmp − regular expression compile/execute

SYNOPSIS

char ∗regcmp(string1[,string2, ...],0);
char ∗string1, ∗string2, ...;

char ∗regex(re,subject[,ret0, ...]);
char ∗re, ∗subject, ∗ret0, ...;

DESCRIPTION

Regcmp compiles a regular expression and returns a pointer to the compiled form.  Malloc(3C) is used to create space for the vector. It is the user’s responsibility to free unneeded space so allocated. A zero 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 zero 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 meanings.

[]*.^ These symbols retain their current meaning. 

$ Matches the end of the string, \n matches the 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 last or first 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.  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.  {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 present, 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 parenthesis.  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 (see regcmp(1)) against string.

This routine is kept in /lib/libPW.a. 

SEE ALSO

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

BUGS

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(3C) re-uses the same vector saving time and space:

/∗ user’s program ∗/
...
malloc(n) {
static int rebuf[256];
return &rebuf;
}

May 16, 1980