If you want to control a link while submitted from a form, how would this functions be used properly?

...What?

preg_match() is a Perl-compatible regex function. It is like ereg(), only the regex is different.

preg_match() basically compares a string against a regular expression pattern. The pattern you write depends on what you want it to do. From the extremely vague description of your post, I can't help you further, except to tell you to look up tutorials on regex (regular expressions).

I found this video helpful when starting to learn regular expressions. http://www.phpvideotutorials.com/regex/ He uses preg_match for most of his examples, and only covers Perl-compatible regular expressions.

According to PHP,

Originally Posted by http://us3.php.net/ereg

Note: preg_match(), which uses a Perl-compatible regular expression syntax, is often a faster alternative to ereg().

This is why I stick with the preg functions.