Help: How replace comma with a tab in a text file?

["Jonathan Gift" <jgift@wanadoo.fr>]

Hi,

I have a comma delimited ex-database file and I want to replace the commas
with tabs. I tried using:

sed s/,/\tab/ filename but no go. It was a guess anyway. I tried replacing
the tab with a * and it worked, but only for first line of items, mleaving
the rest of the fields with commas.

Any suggestions?

Thanks,

Jonathan