Have a look at the preg_match()
PHP function in the manual.
Quick Example:
<?php
// Check if the string is at least 8 chars long
if (strlen($password) < 8)
{
// Password is too short
}
// Make the password "case insensitive"
$password = strtolower($password);
// Create the validation regex
$regex = '/^[a-z][\w!@#$%]+\d$/i';
// Validate the password
if (preg_match($regex, $password))
{
// Password is valid
}
else
{
// ... not valid
}
Regex Explanation:
^ => begin of string
[a-z] => first character must be a letter
[\w!@#$%]+ => chars in between can be digit, underscore, or symbol
\d => must end with a digit
$ => end of string
/i => case insesitive
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solved PHP regex for validating password [closed]