How to validate a username using php
My rules are:
Username can only contain letters, numbers and 1 underscore.
This is my current preg_match
preg_match('/^[a-zA-Z0-9][_]{1}[a-zA-Z0-9]+$/',$_POST['uname'])
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On at least two of your previous questions, you say "thanks", but didn't accept the answer. Go back over your other questions and, if an answer helped you, click the big check mark next to that answer.Herbert– Herbert2011-12-21 16:08:56 +00:00Commented Dec 21, 2011 at 16:08
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1 Answer
This should do it:
/^[a-zA-Z0-9]*_?[a-zA-Z0-9]*$/
Keep in mind that a character class of a single item is redundant. Write the atom solely instead. And {1} is another seriously redundant quantifier.
/[_]{1}/
is just the same as
/_/
Edit:
Based on the new constrains and in the helpful comment by chris, this seems to be a better regex:
/^[a-zA-Z0-9]+_?[a-zA-Z0-9]+$/D
It matches usernames of at least two character, not ending or beginning with the optional underscore, and no newlines at the end.
5 Comments
user1033600
Thanks :D But I have another question, I also need that _ should not be first and last of the username myusername - not allowed myusername - not allowed
sidyll
@user1033600 what's the minimum number of characters allowed?
goat
use the
D flag unless you like usernames with a newline as the last character /^[a-zA-Z0-9]*_?[a-zA-Z0-9]*$/Dsidyll
Sorry @chris I didn't know about this flag. I updated the answer — thanks for pointing it out!
ridgerunner
+1.
^[a-zA-Z0-9]+_?[a-zA-Z0-9]+$ does indeed work. However, a more efficient way of writing this would be: ^[a-zA-Z0-9]+(?:_[a-zA-Z0-9]+)?$ This is much more efficient in declaring a non-match when given longish invalid strings such as: "1234567890123456789012345678901234567890123456789#"