Programming PHP

Table 4-8. POSIX anchors
Anchor Matches
^ Start of string
$ End of string
[[::]] End of word
A word boundary is defined as the point between a whitespace character and an
identifier (alphanumeric or underscore) character:
ereg('[[::]]', 'the Burgundy exploded'); // returns false
ereg('gun', 'the Burgundy exploded'); // returns true
Note that the beginning and end of a string also qualify as word boundaries.
Functions
There are three categories of functions for POSIX-style regular expressions: matching,
replacing, and splitting.
Matching
The ereg( ) function takes a pattern, a string, and an optional array. It populates the
array, if given, and returns true or false depending on whether a match for the pattern
was found in the string:
$found = ereg(pattern, string [, captured ]);
For example:
ereg('y.*e$', 'Sylvie'); // returns true
ereg('y(.*)e$', 'Sylvie', $a); // returns true, $a is array('Sylvie', 'lvi')
The zeroth element of the array is set to the entire string being matched against. The
first element is the substring that matched the first subpattern, the second element is
the substring that matched the second subpattern, and so on.
The eregi( ) function is a case-insensitive form of ereg( ). Its arguments and return
values are the same as those for ereg( ).
Example 4-1 uses pattern matching to determine whether a credit-card number
passes the Luhn checksum and whether the digits are appropriate for a card of a specific
type.
Example 4-1. Credit-card validator
// The Luhn checksum determines whether a credit-card number is syntactically
// correct; it cannot, however, tell if a card with the number has been issued,
// is currently active, or has enough space left to accept a charge.
POSIX-Style Regular Expressions | 101
This is the Title of the Book, eMatter Edition
Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved.