Regex for alphanumeric, but at least one letter
In my ASP.NET page, I have an input box that has to have the following validation on it:
Must be alphanumeric, with at least one letter (i.e. can't be ALL numbers).
Solution 1:
^\d*[a-zA-Z][a-zA-Z0-9]*$
Basically this means:
- Zero or more ASCII digits;
- One alphabetic ASCII character;
- Zero or more alphanumeric ASCII characters.
Try a few tests and you'll see this'll pass any alphanumeric ASCII string where at least one non-numeric ASCII character is required.
The key to this is the \d* at the front. Without it the regex gets much more awkward to do.
Solution 2:
Most answers to this question are correct, but there's an alternative, that (in some cases) offers more flexibility if you want to change the rules later on:
^(?=.*[a-zA-Z].*)([a-zA-Z0-9]+)$
This will match any sequence of alphanumerical characters, but only if the first group also matches the whole sequence. It's a little-known trick in regular expressions that allows you to handle some very difficult validation problems.
For example, say you need to add another constraint: the string should be between 6 and 12 characters long. The obvious solutions posted here wouldn't work, but using the look-ahead trick, the regex simply becomes:
^(?=.*[a-zA-Z].*)([a-zA-Z0-9]{6,12})$
Solution 3:
^[\p{L}\p{N}]*\p{L}[\p{L}\p{N}]*$
Explanation:
-
[\p{L}\p{N}]*matches zero or more Unicode letters or numbers -
\p{L}matches one letter -
[\p{L}\p{N}]*matches zero or more Unicode letters or numbers -
^and$anchor the string, ensuring the regex matches the entire string. You may be able to omit these, depending on which regex matching function you call.
Result: you can have any alphanumeric string except there's got to be a letter in there somewhere.
\p{L} is similar to [A-Za-z] except it will include all letters from all alphabets, with or without accents and diacritical marks. It is much more inclusive, using a larger set of Unicode characters. If you don't want that flexibility substitute [A-Za-z]. A similar remark applies to \p{N} which could be replaced by [0-9] if you want to keep it simple. See the MSDN page on character classes for more information.
The less fancy non-Unicode version would be
^[A-Za-z0-9]*[A-Za-z][A-Za-z0-9]*$