PHP: Remove Everything But Letters And Numbers – Reg Expressions

Jul 15th, 2008
Maruf scribbled this post.

where's wally?

I always forget this PHP function, but I’m finding myself regularly needing it. I thought I’d just jot it down for my own reference and for anyone else who might need it.

Function: ereg_replace

What this function basically does is remove all characters from a string which isn’t a letter or a number. It can be a very cool function for error checking. Regular expression functions like this enable you to search for patterns within a string.

View Code PHP

1
2
3

$string = "remove ever^&amp;thing but *&amp;^*&amp;%£ letters &amp; numbers*&amp;^*";
$cleansedstring = ereg_replace("[^A-Za-z0-9]", "", $string );
echo $cleansedstring;

$cleansedstring should output: removeeverthingbutlettersnumbers

I used “[^A-Za-z0-9]” to remove every chracter that isn’t a letter or number, but here are some different matches:

[abc]	a, b, or c
[a-z]	Any lowercase letter
[^A-Z]	Any character that is not a uppercase letter
(gif\|jpg)	Matches either “gif” or “jpeg”
[a-z]+	One or more lowercase letters
[0-9\.\-]	any number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$	Any word of at least one letter, number or _
([wx])([yz])	wy, wz, xy, or xz
[^A-Za-z0-9]	Any symbol (not a number or a letter)
([A-Z]{3}\|[0-9]{4})	Matches three letters or four numbers

You should note that because regular expressions are more powerful than regular functions, they are also slower. You should only use regular expressions if you have a particular need. Out of curiosity, does anyone know a less taxing function of getting the same result, or are regular expressions the most suitable option for stripping everything but numbers and letters?

For a more indepth explanation, here’s an awesome tutorial on Using Regular Expressions.

UPDATE: 04 Sept, 2009

Thanks to a reader, I’ve been informed about a more efficient way of stripping everything but alphanumeric characters.

View Code PHP

1
2
3

$string = "remove ever^&amp;thing but *&amp;^*&amp;%£ letters &amp; numbers*&amp;^*";
$cleansedstring = preg_replace('#\W#', '' $string);
echo $cleansedstring;

Excellent.

Filed away: PHP

comments

This is actually incorrect.
Your posted example will have the exact opposite effect that you are intending it to here.
Your replace will actually match ALL letters and numbers, and replace them with nothing. Leaving you a string with a bunch of random chars.

Nick Overstreet

Aug 11th, 2008