Question

I am looking for a method of having console auto complete – such that given an application like:

int main (int argc, char ** argv)
{
  if (argc == 1) return EXIT_FAILURE;
  if (strcmp(argv[1], "good")==0) printf("good\n");
  if (strcmp(argv[1], "bad")==0) printf("bad\n");
  return EXIT_FAILURE;
}

When running it, I would like pressing [tab] after the command, such that it would give me one of the possible useful options.

Example:

./a.out g[tab]

would auto complete to

./a.out good

I don’t want to edit /etc/bash-completion.d/, I was hoping for a much stronger auto-complete, something like a function in the executable itself that would be called – perhaps so it could query a database for the list of possible options. Or perhaps output a message letting you know what the options are.

If you think this is simply totally impossible, let me know!

Answer 1

Completions are a property of the shell you run the application from. You will have to provide completion functions for all the shells you want to support (bash, zsh, tcsh and fish have customizable completions). A completion function can call your application (e.g. run you_application --list-possible-arguments) or do whatever it chooses to generate the completions — it’s already a “strong” completion in your terminology.

In bash, you declare completions with the complete built-in. Look in /etc/completion.d for examples (gpg is a fairly simple example; git is a rather involved one).