4.8.1 Basic regexps with preg_match() and preg_match_all()This is NOT the latest copy of this book; click here for the latest version.
int preg_match ( string pattern, string subject [, array matches [, int flags [, int offset]]])
int preg_match_all ( string pattern, string subject [, array matches [, int flags [, int offset]]])
Our basic regexp function is preg_match() and takes two parameters: the pattern to match, and the string to match it against. Preg_match() will apply the regular expression in parameter one to the string in parameter two and see whether it finds a match - if it does, it will return 1, otherwise 0. The reason it returns 1 is because regular expressions return the number of matches found, but preg_match(), for speed reasons, returns as soon as it finds the first match - this means it is very quick to check whether a pattern exists in a string. An alternative function, preg_match_all(), does not exit after the first match - we will get onto that later.
Regular expressions are formed by starting with a forward slash /, followed by a sequence of special symbols and words to match, then another slash and, optionally, a string of letters that affect the expression.
Sound complicated? Don't worry - it is complicated! We're going to break it right down, though, so hopefully it will make sense immediately. Here is a list of very basic regular expressions, strings, and whether or not a match is made:
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Regexp
|
String
|
Result
|
|
/php/
|
php
|
Match
|
|
php/
|
php
|
Error; you need a slash at the start
|
|
/php/
|
PHP
|
No match; regexps are case sensitive
|
|
/php/i
|
PHP
|
Match; /i means "case insensitive"
|
|
/Foo/i
|
FOO
|
Match
|
As you can see, "i" is the modifier to make the regexp case insensitive - it will slow things down a touch, but might make your life a great deal easier.
Here is how to use preg_match() on some of those example regexps:
<?php
if (preg_match("/php/", "php")) {
print "Got match!\n";
}
if (preg_match("/php/", "PHP")) {
print "Got match!\n";
}
if (preg_match("/php/i", "php")) {
print "Got match!\n";
}
?>
The first and third preg_match() calls will return true (the second will fail because the case is wrong and "i" is not specified), and print "Got match!"
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