Regex for alphanumeric, but at least one letter

^\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.

^[\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]*$