Regular expression also known as regex or regexp is a sequence of characters that forms a search pattern. It is used by most of the programming language like php, javascript, perl etc.
Here is the list of most useful regular expressions for webmasters. To test them on text string use our Regular expression testing tool.
Regular expression for username
Following pattern will match alphanumeric string including “_” of length 3 to 16.
^[a-z0-9_]{3,16}$
Regular expression for email
^[a-z0-9]+[_a-z0-9.-]*[a-z0-9]+@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,4})$
Regular expression for URL
^http[s]?://[a-z0-9-.]+.[a-z.]{2,5}(/[a-z0-9%-_.?=&@#]*)?$
Regular expression for Domain Name
^[a-z0-9]+[a-z0-9-.]*[a-z0-9]+.[a-z.]{2,5}$
Regular expression for IP-address
This will match any IP-address between 0.0.0.0 to 255.255.255.255
^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]).){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$
Regular expression for Decimal value
Following pattern will match any decimal digit of any size.
^[0-9]+$
Regular expression for Float value
This will match any floating point value eg 1.2, 2.009 or .987 but not match 1.00 or 239
^[0-9]*.[0-9]*[1-9]+$
Regular expression for Hexadecimal color
This Regex pattern will match any 3 or 6 digit hexadecimal value eg: FF2 or 33CCEE
^([a-f0-9]{6}|[a-f0-9]{3})$