I was trying to create a php code to parse some text and to process it.

I have difficult time with the substr (sub string), strpos (which return the position of a particular segment of string). Testing and debugging it is just a time consuming work.

Luckily my friend enlighten me by introducing me regular expression way to look for values in a text. Using regular expressions you can easy find a pattern in a string and/or replace it if you want.

BUT PHP regular expressions seems to be a quite complicated area especially when I am not a experienced Unix user.Historically regular expressions were originally designed to help working with strings under Unix systems.

The regular expressions basic syntax

To use regular expressions first you need to learn the syntax of the patterns. We can group the characters inside a pattern like this:

  • Normal characters which match themselves like hello
  • Start and end indicators as ^ and $
  • Count indicators like +,*,?
  • Logical operator like |
  • Grouping with {},(),[]

An example pattern to check valid emails looks like this:

Code:


^[a-zA-Z0-9._-]+@[a-zA-Z0-9-]+\.[a-zA-Z.]{2,5}$

The code to check the email using Perl compatible regular expression looks like this:
  1. $pattern = “/^[a-zA-Z0-9._-]+@[a-zA-Z0-9-]+\.[a-zA-Z.]{2,5}$/”;
  2. $email = “abcd@mydomain.com”;
  4. if (preg_match($pattern,$email)) echo “Match”;
  5. else echo “Not match”;
The syntax is not easy derive when you are not familiar with it. After googling around, I found http://regex.larsolavtorvik.com
This AJAX tool allows you to enter sample text string and your pattern string. The tool is able to execute it on the fly and shows result immediately. It will also print out the PHP source code. This really save my time from hard coding pattern and test string.



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