How do I write a regex in PHP to remove special characters?

Question

Hi, I'm pretty new to PHP, and I noticed there are many different ways of handling regular expressions.

This is what I'm currently using:

$replace = array(" ",".",",","'","@");
$newString = str_replace($replace,"_",$join);

$join = "the original string i'm parsing through";

I want to remove everything which isn't a-z, A-Z, or 0-9. I'm looking for a reverse function of the above. A pseudocode way to write it would be

'If characters in $join are not equal to a-z,A-Z,0-9 then change characters in $join to "_"'

Answer 1

The regular expression for anything which isn't a-z, A-Z, 0-9 is:

preg_replace('/[^a-zA-Z0-9]/', "_", $join);

This is known as a Negated Character Class

Answer 2

$newString = preg_replace('/[^a-z0-9]/i', '_', $join);

This should do the trick.

Answer 3

I am not giving you the answer but this tutorial is well worth its 10 minutes.

Link to Regular Expressions in PHP

Answer 4

The easiest way is this:

preg_replace('/\W/', '_', $join);

\W is the non-word character group. A word character is a-z, A-Z, 0-9, and . \W matches everything not previously mentioned.

Edit: preg uses Perl's regular expressions, documented in the perlman perlre document.

*Edit 2: This assumes a C or one of the English locales. Other locales may have accented letters in the word character class. The Unicode locales will only consider characters below code point 128 to be characters.