Question

I’m trying to check if a string has a certain number of occurrence of a character.

Example:

$string = '123~456~789~000';

I want to verify if this string has exactly 3 instances of the character ~.

Is that possible using regular expressions?

Answer 1

As single character is technically a substring, and the task is to count the number of its occurences, I suppose the most efficient approach lies in using a special PHP function – substr_count:

$string = '123~456~789~000';
if (substr_count($string, '~') === 3) {
  // string is valid
}

Obviously, this approach won’t work if you need to count the number of pattern matches (for example, while you can count the number of ‘0’ in your string with substr_count, you better use preg_match_all to count digits).

Yet for this specific question it should be faster overall, as substr_count is optimized for one specific goal – count substrings – when preg_match_all is more on the universal side. )