PHP regular expressions examples

The regular expression, as a pattern, can match all kinds of text strings helping your application validate, compare, compute, decide etc. It can do simple or very complex string manipulations. The list of possibilities is enormous when it comes to what you can achieve using regular expressions. You can take any phrase that starts with an "A" or any character and do various things with it. You can match phone numbers, email addresses, url's, credit card numbers, social security numbers, zip codes, states, cities.....(the list never ends). A huge script that is supposed to validate a user input and prepare it for sql can be reduced to only one line with the help of preg_replace.