php code to validate alphanumeric string

I want to validate alphanumeric string in form text box in php. It can contain numbers and special characters like '.' and '-' but the string should not contain only numbers and special characters. Please help with the code.


Try this

// Validate alphanumeric
if (preg_match('/^[a-zA-Z]+[a-zA-Z0-9._]+$/', $input)) {
    // Valid
} else {
    // Invalid

Use ctype_alnum like below:

    echo "Yes, It's an alphanumeric string/text";
    echo "No, It's not an alphanumeric string/text";

Read function specification on


if(preg_match('/[^a-z_\-0-9]/i', $string)) { echo "not valid string"; }


  • [] => character class definition
  • ^ => negate the class
  • a-z => chars from 'a' to 'z'
  • _ => underscore
  • - => hyphen '-' (You need to escape it)
  • 0-9 => numbers (from zero to nine)

The 'i' modifier at the end of the regex is for 'case-insensitive' if you don't put that you will need to add the upper case characters in the code before by doing A-Z

I'm sort of new to regex, but I would do it this way:

preg_match('/^[\w.-]+$/', input)

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