AutoComplete for a command line processor works like the following: suppose
you have two files file1.c and happy.h under the current directory. You
want to edit file1.c, then you type in "vim" :-)), space, "f", and then
press TAB, the commandline processor should fill in "ile1.c" for you, since
it only finds one file under the current directory starting with "f".
Another usage: if you have three programs in your path: cmd1, happy2, t3,
and you want to run happy2, then you type in "h" and press