I don't quite have full completion, but I do wrap Mathematica in GNU rlwrap. I know that you can teach rlwrap a list of keywords to autocomplete, and even program it to determine what completions to suggest from your context. At the very least, you get history and line editing out of it.

My recipe:

• I used MacPorts to install rlwrap, and their port seems to work fine.
• Then I added alias math='rlwrap /Applications/Mathematica\ Home\ Edition.app/Contents/MacOS/MathKernel' to my login script.
  • Obviously, it might live in a different place if you use a different edition of Mathematica than I do.

I don't quite have full completion, but I do wrap Mathematica in GNU rlwrap. I know that you can teach rlwrap a list of keywords to autocomplete, and even program it to determine what completions to suggest from your context. At the very least, you get history and line editing out of it.

My recipe:

• I used MacPorts to install rlwrap, and their port seems to work fine.
• Create a list of Mathematica definitions that you care about and put it in ~/mathdefs.txt.
• Then I added alias math='rlwrap -r -f ~/mathdefs.txt /Applications/Mathematica.app/Contents/MacOS/MathKernel' to my login script.
  • The -r tells it to remember words that it sees you type during a session, and the -f ~/mathdefs.txt seeds its completion support with the words that you put in that file.

I notice that Wolfram has added their own history/editing support (probably using readline) in 10.1 at least. Quite possibly before then. I'm sure it wasn't there in 8.0, and I don't think it was in 9.0, but I'm not positive.