Regex for a file name without an extension

Question

I'm looking for a regex expression that will capture a file name that does not have an extension and give me that name in a backreference so I can add an extension. So if someone puts in xyz I can replace it with xyz.html. xyz.php or xyz.html should not be captured.

Thanks

Answer 1

Assuming the extensions are up to 4 chars in length (so filenames like mr.smith aren't considered as having an extension, but mr.smith.doc and mr.smith.html are considered as having extensions):

^.*[^.]{5}$

No need to capture a group, as the whole expression is what you want - ie group 0.

Answer 2

Use following regular expression:

^([^.]+)$

meaning filename that only consist of non-dot characters.

UPDATE

added paren for capturing group.