You might want to use the '-r' option to tell sed to use extended regular expressions. Basic sed regexes are quite limited.

Second, regular expressions work differently in sed than they do in a shell. * doesn't mean anything by itself, it's a modifier for something else. First you tell it what expression you want to match, then optionally, how many of them you want to match. An expression can be a single letter, a set of letters, or something in brackets.

• A by itself just matches the letter A, like you'd expect.
• [ABC] by itself just matches the letter A, B, or C.
• A* tells it to match 0 or more A characters.
• [ABC]* tells it to match 0 or more characters among A, B, C.
• [A-Z]* tells it to match 0 or more characters among A, B, C, ..., Z.
• [^A]* tells it to match 0 or more characters that aren't A.
• (ABC)* tells it to match 0 or more repititions of "ABC".

* is not the only modifier:

• A+ tells it to match 1 or more A characters.
• A? tells it to match 0 or 1 A characters.
• A{4} tells it to match precisely 4 A characters.