I need to change a string from a format such as
abcdefghijklmnopqrstuvwxyz to ab/cd/ef/abcdefghijklmnopqrstuvwxyz.

What is the most efficient way to do this in php?

Examples:

123456789 would become 12/34/56/123456789

gwn58yh045bgw0r8 would become gw/n5/8y/gwn58yh045bgw0r8

You want preg_replace. This code should do it:

$input = 'abcdefghijklmnopqrstuvwxyz';
$output = preg_replace('/^(..)(..)(..).*$/', "$1/$2/$3/$input", $input);

This take the first 3 groups of two characters (..) and prepends them ($1, $2, $3) to the original string, with slashes.

Demo: http://codepad.org/WueutXZA

more