Inverting Character Sets in Regex

Using the caret ^ at the beginning of square brackets allows you to invert the desired set. That is, if, for example, the pattern [ab] searches for the letter 'a' or 'b', then the pattern [^ab] will search for all characters except 'a' and 'b'.

Example

In this example, the search pattern looks like this: letter 'x', then NOT letter 'a', not 'b' and not 'c', then letter 'z':

php<?php
  $str = 'xaz xbz xcz xez';
  $res = preg_replace('#x[^abc]z#', '!', $str);
?>

As a result, the following will be written to the variable:

php'xaz xbz xcz !'

Example

In this example, the search pattern looks like this: letter 'x', then NOT a lowercase Latin letter, then letter 'z':

php<?php
  $str = 'xaz xbz x1z xCz';
  $res = preg_replace('#x[^a-z]z#', '!', $str);
?>

As a result, the following will be written to the variable:

php'xaz xbz ! !'

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