I've this PHP regular expression:
$username = preg_replace('/[^a-z0-9]/i', '', $username);
It allows only A-Z and 0-9. How can I allow ., - and _ as well?
views:
102answers:
7
+1
A:
$username = preg_replace('/[^a-z0-9._-]/i', '', $username);
Removes anything that isn't ([^]) one of the characters on the group. Note the hypern is the last one there, so it loses its special meaning.
Kobi
2010-03-01 09:37:54
I always thought a hyphen only meant something when between letters or numbers - what would `$username = preg_replace('/[^_-.]/i', '', $username);` do?
Dominic Rodger
2010-03-01 09:41:12
it will mind characters **between** `_` and `.`, which is just weird.
Kobi
2010-03-01 09:42:14
@Kobi - interesting - so presumably all characters with decimal values between 95 (`_`) and 46 (`.`)? Wonder if that would equate to `.-_`.
Dominic Rodger
2010-03-01 09:43:53
Also, someone checked and found that `/[^a-z0-9._-]+/i` is better here, but that's optimizing.
Kobi
2010-03-01 09:54:51
+1
A:
If you know exactly what you need to match, just specify it in a character group. The dash either needs to be at the very start or very end.
/[A-Z0-9._-]/
ar
2010-03-01 09:38:18
In the answer that was deleted, you said that escaping the DOT will cause the backslash to be matched too, this is not true. Try it: `preg_match_all('/[\.]/', '.\\', $matches); print_r($matches);` Adding a single backslash does nothing, it will just match the literal DOT inside a character class.
Bart Kiers
2010-03-01 09:45:09
+1
A:
$username = preg_replace('/[^a-z0-9._-]/i', '', $username);
Your current code actually does allow both A-Z and a-z - the i flag marks your regular expression as case-insensitive.
Dominic Rodger
2010-03-01 09:38:25
+6
A:
You can use the following regex:
/[^a-z0-9._-]/i
- i at the end is to make the pattern
matching case-insensitive. You can
drop it and use:
/[^a-zA-Z0-9._-]/ - -(hyphen) has a special meaning in char class if its surrounded on both
sided so we put it at the end so that
its treated literally. You can also
do:
/[^a-z0-9.\-_]/where we are escaping the hyphen - A dot in a char class is not a meta char hence will be treated literally and need not be escaped.
codaddict
2010-03-01 09:38:37
+2
A:
Try
$username = preg_replace('/[^a-z0-9.-_]/i', '', $username);
Jojo Sardez
2010-03-01 09:39:34
+1
A:
Easy, just add those characters to the regular expression as well
$username = preg_replace('/[^a-zA-Z0-9._-]/','',$username)
The . needs to be escaped because its the 'matchall' character, the - goes in the end because otherwise it would be used to define a range (we could ofcourse have just escaped it).
Kristoffer S Hansen
2010-03-01 09:40:59