Bash completion for custom command to complete static directory tree

Question

I would like to add a custom completion spec for bash's Programmable Completion that does the following: whenever the command entered is foo, I would like to do filename/directory completion for the partial token after foo, but relative to a fixed directory (say /a/b/c) rather than the current working directory.

For example, suppose /a/b/c contains the files

hello goodbye cheers directory

and /a/b/c/directory contains the files

adieu ciao

Then, typing foo go<TAB> should complete go to goodbye, and typing foo dir<TAB>ci<TAB> should complete the argument first to directory/ and then to directory/ciao, regardless of what my current working directory is.

I was hoping to be able to set this up with just a single call to complete, but after reading the manual, it doesn't appear that I can do this. Can it be done? And, if not, how could I add a compspec to do this?

Answer 1

You could use a custom completion function like the following:

_foo () { 
  local cur
  COMPREPLY=()
  cur=${COMP_WORDS[COMP_CWORD]}
  k=0
  i="/a/b/c" # the directory from where to start
  for j in $( compgen -f "$i/$cur" ); do # loop trough the possible completions
    [ -d "$j" ] && j="${j}/" || j="${j} " # if its a dir add a shlash, else a space
    COMPREPLY[k++]=${j#$i/} # remove the directory prefix from the array
  done
  return 0
}

And then register the function to be used with your command foo:

complete -o nospace -F _foo foo