bash substring substitution

I just came across this today, it's something that I wish I'd known years ago (I think it just shows that I need to read more manuals), I've been emulating this feature with Perl and regexes or with the basename/dirname commands.

It's very simple; today I wanted to run through a set of files with a particular file extension, do some processing and then print the output to another file named the same as the original but with a different extension.

So, say the files are .tsv (tab delimited) and I want to create a .csv (comma delimited) one from the first two columns, you can do it like this:

for file in `ls *.tsv`;
  do cut -f1,2 --output-delimiter=, \
  $file > ${file/.tsv/.csv};
done

Sweet, eh?