Regex - How to replace period in file name with an underscore

Question

I'm looking to build a regular expression that will allow me to replace the periods (.) in a filename with an underscore (_).

Example: replace filename.doc with filename_doc

I've had a play around in Expresso, and have worked out that it will be something like .\w{3,4) - to pick up 3 or 4 character extentions eg doc, docx, xls, xlsx etc.

But I cannot figure out how to replace only the period and retain the extention.

Answer 1

You have to escape . sign. Try with following regex:

\.(\w{3,4})$

And replace it with:

_$1

$1 contains matched string in ()