REGEX for any file extension

Question

I am trying to build a regex to tell if a string is a valid file extension. It could be any extentions.

hello        no
.hello       Yes
..hello      No
hello.world  No
.hello.world No
.hello world No

I have tried ^\. and ^\.[\.] but can't get what i am looking for. This seems like it should be simple.

Answer 1

^\.[^.]+$

This means start with . and then anything other than dot (.)

You can also use this one if you want to have only aplhanumeric.:

^\.[a-zA-Z0-9]+$

Answer 2

Try this regex:

^\.[\w]+$

Matches a string starting with a ".", followed by one or more "word" character(s), until the end of the string.