8 Practical PHP Regular Expressions

Validating a Username:

Quote: Something often overlooked, but simple to do with a regular expression would be username validation. For example, we may want our usernames to be between 4 and 28 characters in length, alpha-numeric, and allow underscores. PHP Code: $string = "userNaME4234432_";
if (preg_match('/^[a-z\d_]{4,28}$/i', $string)) {
echo "example 1 successful.";
}
Telephone Numbers:

Quote: Number in the following form: (###) ###-#### PHP Code: $string = "(232) 555-5555";
if (preg_match('/^(\(?[0-9]{3,3}\)?|[0-9]{3,3}[-. ]?)[ ][0-9]{3,3}[-. ]?[0-9]{4,4}$/', $string)) {
echo "example 2 successful.";
}
Emails:

PHP Code: $string = "first.last@domain.co.uk";
if (preg_match(
'/^[^0-9][a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*[@][a-zA-Z0-9_]+([.][a-zA-Z0-9_]+)*[.][a-zA-Z]{2,4}$/',
$string)) {
echo "example 3 successful.";
}
Postal Codes:

PHP Code: $string = "55324-4324";
if (preg_match('/^[0-9]{5,5}([- ]?[0-9]{4,4})?$/', $string)) {
echo "example 4 successful.";
}
Ip Address:

PHP Code: $string = "255.255.255.0";
if (preg_match(
'^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.](?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$',
$string)) {
echo "example 5 successful.";
}
Hexadecimal Colors:

PHP Code: $string = "#666666";
if (preg_match('/^#(?:(?:[a-f\d]{3}){1,2})$/i', $string)) {
echo "example 6 successful.";
}
Multi-line Comments:

PHP Code: $string = "/* commmmment */";
if (preg_match('/^[(/*)+.+(*/)]$/', $string)) {
echo "example 7 successful.";
}
Dates:

Quote: MM/DD/YYYY format PHP Code: $string = "10/15/2007";
if (preg_match('/^\d{1,2}\/\d{1,2}\/\d{4}$/', $string)) {
echo "example 8 successful.";
}
Some might be more/less useful than the others but that will depend on the project you are working on.