Common validation regular expressions

All regular expressions are tested with php function eregi
Validate E-Mail

Username can contain letters, numbers, and dots

^([-a-z0-9._]{2,32}@([a-z0-9-]{1,64}[.]){1,5}([a-z0-9]){2,6}$|$)

Validate URL

Domain can contain letter, numbers and dashes. HTTP://, HTTPS:// and FILE:// allowed

^((http://|https://|file://){0,1}([a-z0-9-]{1,32}[.]){1,10}([a-z0-9]){2,3}(:[0-9]{1,5}){0,1}([/\]{1,3}[a-z0-9_-~.]{0,64}){0,16}([?][a-z0-9=%;+]+){0,1}$|$)

Example usage of url validation regular expression would go something like this (php):

if (!eregi("^((http://|https://|file://){0,1}"    // type
.'([a-z0-9-]{1,32}[.]){1,10}([a-z0-9]){2,3}'  // domain
.'(:[0-9]{1,5}){0,1}'				       // port
.'([/\]{1,3}[a-z0-9_-~.]{0,64}){0,16}'	       // directory
.'([?][a-z0-9=%;+]+){0,1}$|$)',		         // options
trim($url_to_validate))) echo "url not valid";
else echo "url is valid";

Validate Date/Time

Will check date/time in format ‘yyyy-m-d h:m:s’

^([0-9]{4})[-/.]([0-9]{1,2})[-/.]([0-9]{1,2}) ([0-9]{1,2})(:[0-9]{1,2})(:[0-9]{1,2}){0,1}$

To fully validate date/time input you might want to use something like this:

function datetimeValidation($datetime) {
    if (eregi('^([0-9]{4})[-/.]([0-9]{1,2})[-/.]([0-9]{1,2}) ([0-9]{1,2})(:[0-9]{1,2})(:[0-9]{1,2}){0,1}$', trim($datetime), $t))
	if (checkdate($t[2], $t[3], $t[1]))
	    if (($t[4] < 24)&&($t[5] < 60)&&($t[6] < 60))
		return sprintf('%04d-%02d-%02d %02d:%02d:%02d', $t[1], $t[2], $t[3], $t[4], $t[5], $t[6]);
    return false;
}