(PHP 4 >= 4.0.3, PHP 5)
escapeshellarg — Escape a string to be used as a shell argument
escapeshellarg() adds single quotes around a string and quotes/escapes any existing single quotes allowing you to pass a string directly to a shell function and having it be treated as a single safe argument. This function should be used to escape individual arguments to shell functions coming from user input. The shell functions include exec(), system() and the backtick operator.
The argument that will be escaped.
The escaped string.
Example#1 escapeshellarg() example
<?php
system('ls '.escapeshellarg($dir));
?>