[SOLVED] Really quick regex question

[speaker219]

In php, how would i validate a form so that it can only be letters and numbers? Thanks. (have no idea how to write regex expressions)

If possible, could you show me exactly how to do it in php so i could return a message if it is not validated correctly? thanks.

[btherl]

if (preg_match('|^[0-9a-z]*$|i', $_REQUEST['field'])) {
  print "Yup that's valid";
} else {
  print "Nope, that ain't valid";
}

 

The regexp matches "0 or more characters from 0-9 or a-z, ignoring case, starting at the start and ending at the end".  If there's any character not in those ranges then it can't match, because it must start at the start and end at the end (which is the meaning of ^ and $).