Completing a command like another command in bash

A fake answer appears insufficient for this fake question; the zsh builtin support for automount directories operates on directories (fake-files dir:names), and not on file patterns therein. This is handy to add specific named files to a directory, which may suit automount or sshfs or NetApp .snapshot type setups where the directory-to-be-mounted is a known static name, ALAS.

autoload -U compinit
compinit
zstyle ':completion:*' fake-files $HOME/.avfs:'ALAS POOR YORICK'

zshall(1) says the "names" are strings, and experiments indicate metacharacters (e.g. # or \# or '*(e:"echo hi":)') "do not work" in various ways, so there is no way I know of to sneak a glob onto the names portion of the fake-files statement. (Delving through Src/Zle/computil.c might reveal exactly what the names can be, but that would be more work.) (Also, using recursive globs in the directory position to name archive files did not fly, but again it will take C diving to see how much fake-files lets you get away with.)

With compdef, one can list the .avfs directory completions:

compdef '_files -g $HOME/.avfs/\*' -p \^
function andthehash {
  reply=($REPLY $REPLY\#)
}
compdef "_files -g $HOME/.avfs/'*(+andthehash)'" -p \^

Except this fails, as it will only show the # files when it does not matter, and thus cannot complete on them. (There are productive uses for this form, though not for this case.)

Using zstyle gets you closer, with the following .zshrc:

autoload -U compinit
compinit

function UnderAVFS {
  local pdir
  [[ -z $1 ]] && return 1
  pdir=$1:a
  [[ ! -d $pdir ]] && pdir=$pdir:h
  [[ ! -d $pdir || $pdir == . ]] && return 1
  while [[ $pdir != / ]]; do
    [[ $pdir == $HOME/.avfs ]] && return 0
    pdir=$pdir:h
  done
  return 1
}

function AVFSExtras {
  if UnderAVFS $REPLY; then
    reply=($REPLY)
    # TODO embiggen list of archive suffixes
    [[ $REPLY == *.(bz2|tbz2) ]] && reply+=($REPLY\#)
  fi
}

# Try to match avfs, otherwise the default pattern. Probably could greatly
# benefit from caching, to avoid hits on UnderAVFS function.
zstyle ':completion:*' file-patterns '*(+AVFSExtras):avfs-files' '%p:all-files'

However, it can only complete up to the \#/ bit (on a debian squeeze virt with a default avfs setup), but not into the virtual filesystem for an archive, so additional work will be necessary to tab complete into the archives. I'm guessing via _call_program ... ls or something along those lines for completions at the \# bit, unless there's a more elegant way to con zsh into believing that directories that do not exist do.

Bad news! The completion does not make it through _path_files for the fake directories; I suspect this is zsh globbing related. Both zsh 4.something on and zsh 5.0.8 exhibit the problem. So I suspect that a complete fix would require patches to _path_files, or to write something different that otherwise completes on these fake dirs. A completion debugging trace can be generated by typing in ls /root/.avfs/root/sometar.gz\#/ and then at the end of that typing control-x and then ?, assuming bindkey -e and that _complete_debug is bound to said keycombo, if someone wants to delve through why this is failing.

Those are commands. If you start typing on the commandline and hit Tab, it won't expand the subdirectories and files of your location but available commands.

Basically, tab completion is context sensitive. If you just start writing and hit Tab, it will complete commands found in your $PATH. If you have already written a command, cd for example, it will complete the files and directories in your current location. For some commands, it will also complete available options to that command.