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How can I tweak zsh's completion system to complete “fake” files in some circumstances?

More precisely, the AVFS filesystem exposes archives as directories by creating a “fake directory” next to every archive. By default, it replicates the whole directory hierarchy under its mount point ~/.avfs. Furthermore, under ~/.avfs, for every archive file such as /tmp/foo.zip, besides the archive file itself ~/.avfs/tmp/foo.zip, there is a directory called ~/.avfs/tmp/foo.zip# which exposes the content of the archive. However this extra directory does not appear in the listing of ~/.avfs/tmp: it only exists when explicitly requested. (This is similar to how some automounters operate.)

cd ~/.avfs/tmp/foo.zip\#

When I type a command like the one above, foo.zip# doesn't appear as a completion under ~/.avfs/tmp/, since there is no such directory. How can I tell zsh that whenever there is a file whose full path $arc matches ~/.avfs/**/*.(tgz|zip)¹, it should pretend that there is a directory called ${arc}#?

(Note that I want the completion to work with every call to _files or _dirs, not just for the cd command. I'd prefer not to have to duplicate the code of the _files function, if possible.)

¹ and all the rest of the extensions

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Does ~/.avfs contain a "copy" of the whole file-system? –  richard Jun 16 '14 at 14:13
@richard Yes, every /path/to/foo is visible as ~/.avfs/path/to/foo. –  Gilles Jun 16 '14 at 15:46
This might be easier fixed in avfs. If it presented the default # directory entry for any files that matched the strings it supports, or even magic tested the files in a directory for what needed to have a # entry, then the completion would just work. I guess there would be a performance hit for something like find as it would now trawl through compressed files. –  Matt Jul 21 '14 at 14:56

1 Answer 1

In zsh you can use compctl -K to register your own function to generation completion options. For example:

compctl -f -c -u -r -K myAVFScompletion "*" -tn

Then you need to define your own function:

myAVFScompletion () {
    read -c COMMAND ARGS

    # Decide what paths you want to suggest completion for
    # by looking inside the ~/.avfs folder.

    # Place your suggestions into an array:
    reply=( a_path b_path ... )

Obviously the above needs some more work, but it's something to start with.

A similar (but different) custom completion function can be registered for bash.

Here is an example with implementations for bash and zsh. (It offers completion of command-line options by grabbing the options out of the command's man page.)

And here are some quick guesses at things that might work inside your completion function:

if [[ -d "$ARGS#" ]]
then reply=( "$ARGS#" )
else reply=

Or perhaps this:

reply=( $(find ~/.avfs -type f -name "*.tgz" -or -name "*.zip" | sed 's+$+#+') )

Good luck!

share|improve this answer
I know how to write a completion function, thank you very much. The problem is how to modify the existing completion mechanism for files. Note that I use the “new” completion mechanism, not compctl, i.e. I want to change what _files does. Your answer is not helpful at all. –  Gilles Jun 5 at 12:52
@Gilles Not to start a flame war, and at the risk of coming off wrong, at least he tried... This has been sitting in the unanswered "attic" 2 years plus... +1 t reset to 0 for the effort. –  eyoung100 Jul 24 at 21:59
@eyoung100 Please do not give +1 for effort (not that effort is apparent here). Upvoting unhelpful answers is detrimental to the site. –  Gilles Jul 24 at 22:26

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