PHP - regex to allow letters and numbers only
1. Use PHP's inbuilt ctype_alnum
You dont need to use a regex for this, PHP has an inbuilt function ctype_alnum which will do this for you, and execute faster:
<?php$strings = array('AbCd1zyZ9', 'foo!#$bar');foreach ($strings as $testcase) { if (ctype_alnum($testcase)) { echo "The string $testcase consists of all letters or digits.\n"; } else { echo "The string $testcase does not consist of all letters or digits.\n"; }}?>2. Alternatively, use a regex
If you desperately want to use a regex, you have a few options.
Firstly:
preg_match('/^[\w]+$/', $string);\w includes more than alphanumeric (it includes underscore), but includes allof \d.
Alternatively:
/^[a-zA-Z\d]+$/Or even just:
/^[^\W_]+$/
You left off the / (pattern delimiter) and $ (match end string).
preg_match("/^[a-zA-Z0-9]+$/", $value)
- Missing end anchor $
- Missing multiplier
- Missing end delimiter
So it should fail anyway, but if it may work, it matches against just one digit at the beginning of the string.
/^[a-z0-9]+$/i