For example I have a link `http://www.abc.com/123/def/ghi/jkl.mno`.
I want to download it using `wget` or `curl` and get the name of output file as `def_ghi_jkl.mno`, where the part `def_ghi` is taken from the link.

I will put this `wget` command in a script to download multiple files so it can't be giving the output file name explicitly.