PHP - Search string for unwanted characters-CodePudding

I am making register script and I need to protect string from characters other than a-z, A-Z, 0-9, and _. Is there simple way to e.g. search string for characters that are NOT in my array of allowed characters?

CodePudding user response：

You could perform a search with a regular expression:

preg_match_all('/[^A-Za-z0-9_]/', $string, $matches);

See preg_match_all for more details.

Basically you are searching for characters, which are not present in the indicated list. The matches are stored in $matches. If the returned array is empty, the string passes, otherwise the array contains the disallowed characters.

CodePudding user response：

This is usually done by means of a regular expression, which allows to search within sets of characters:

<?php
$input = [
  "abcde",
  "XXX111XXX",
  "o",
  "l#QW E, ???P#WE094<SDF",
  "```",
  "GGGG#",
  "",
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
];

$output = array_filter($input, function($value) {
  return preg_match('/^[a-zA-Z0-9] $/', $value);
});

var_dump($output);

The output obviously is:

array(4) {
  [0]=>
  string(5) "abcde"
  [1]=>
  string(9) "XXX111XXX"
  [2]=>
  string(1) "o"
  [7]=>
  string(62) "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
}