processing text files: which tools?

Hi, I need to process a textfile, but don't know which tools to use, need some insight: The original text format is like this: 1,2,3,4,5 1,2,4,5,6 Now I need to insert something (maybe a line or more) before each line which contains the last token. Also, the last token should be in new line, so the format is something like this: some new lines bla blab la 5 blabla 1,2,3,4 5 some new lines 6 blabla 1,2,4,5 6 which tools I need to use? I know / have a little experience with sed, but that's as far as replace/insert character in a lines, not inserting new lines...? TIA -- Verdi March -- __________________________________________________ Do You Yahoo!? Yahoo! Movies - coverage of the 74th Academy Awards� http://movies.yahoo.com/