When you type sub mage foo and hit Tab, you're running the command sub-mage --complete foo. You can check the value of "$2" inside your completion conditional and output a different set of completions there.

We should probably have this as a documented example in the README :)

Great, thanks @sstephenson =]
And +1 on adding this to the README

I attempted that, and it still didn't work, I don't want to be a bother here, but is it possible to do this?
Here is my code:

# Provide sub completions
if [ "$1" = "--complete" ]; then  
  if [ "$2" = "foo" ] || [ "$2" = "bar" ]; then
    { echo baz; echo bla; } | sort | uniq
  else
    { echo foo; echo bar; } | sort | uniq
  fi
  exit;
fi

I even tried adding:

echo $#

But it always shows 1 no matter how many parameters before the <tab>

Thanks in advance, again.

Confirmed. Seems like params beyond the first are not being passed to the sub-commands during auto-complete. Verified by dumping:

echo "Params: $1 $2 $3" >&2

in the first line of my auto-complete conditional and then trying it to do auto-complete with multiple args:

sub command <TAB>
sub command arg1 <TAB>
sub command arg1 arg2 <TAB>

The params only ever contain --complete.

Yep, can confirm also.