This is better as a Perl one-liner:

perl -i.bak -pe 's/,//g' comma
[download]

Now the file comma will have the commas removed and the original file is copied to comma.bak

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)