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How Bash Completion Works

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Re: How Bash Completion Works

#21

Post by vunie »

My issue with bash completion is that it requires a completion script (i.e executing `complete`) for each command you want it to complete. The shell cannot automatically deduce appropriate completions when possible.

This problem is not specific to bash. Fish and other shells can't automatically complete commands either. There is simply no standard way to detect what type of auto-completion a command supports.

I know this comment is a not about the OP, but I've wasted so much time dealing with this that I feel compelled to post this here. I wish shell developers would form some sort of consortium (like XDG) where they can agree on standard solutions to issues like this. No one benefits from having developers waste time manually writing and testing completion scripts for each project (times the number of shells they want to support).

Side note: I remember that there was a project that modified bash internals to detect automatic completion support. It did this by scanning for the presence of a magic string in the first N bytes of a file (or in some ELF section of a binary). If that magic string was present, bash would automatically generate a completion set by passing `--_complete` to the command. I think this is a simple and elegant solution to this problem and one I hope shell developers would consider.

Re: How Bash Completion Works

#22

Post by jolmg »

nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

> 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds.

I've had this happen to me. Would be nice if it could be interrupted with Ctrl-C. My workaround has been to wrap the argument that's triggering that in quotes (when redoing the command in another terminal).

> 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player command tab-completes and only "sees" the mp3, but I actually wanted to know that the .txt was there as well (and in some cases, open it with the media player!)

Maybe a keybinding can be added to enable/disable "smart" completion (leaving only simple filepath completion). Seems like it should be a relatively quick configuration fix.

My workaround for this, for when I want simple filepath completion, has been to prefix the command with `echo`. With vi keybindings it's just `Iecho A` (it's faster if you make your CapsLock an Esc); with emacs keybindings it's `echo `. Afterwards, to delete the `echo`, it's `^dwA` with vi keybindings and `` with emacs keybindings.

> 3. When the completion has a wrong view of the options provided by a program (e.g. completion is not aware of some useful options). Instead of looking at the man-page, I've been tricked by a bad completion-set.

Maybe the list of options could be parsed out of manpages and --help output. Then, it would coincide.

Re: How Bash Completion Works

#23

Post by ciupicri »

nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

Regarding (2), I hate the completion for fdisk [1]. It filters device filenames starting with /dev/disk/{by-id,by-path} even if those names make it easy to select a particular disk.

[1]: https://github.com/karelzak/util-linux/blob/master/bash-comp...

Re: How Bash Completion Works

#24

Post by giancarlostoro »

nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

I use Fish for that kind of thing. I dont write shell scripts for Fish thats what I use Bash for (portability) but Fish has intelligent auto complete hints.

Re: How Bash Completion Works

#25

Post by SPBS »

nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

Yeah homebrew does that remote lookup thing when I try to complete `brew install xx`. Because of the delay, it's not a good way to discover packages at all especially if the package name has an unexpected prefix that causes bash completion to fail. Much better to just `brew search xx` then browse the entire list of possible candidates than to rely on tab completion.

Re: How Bash Completion Works

#27

Post by bobbylarrybobby »

nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

Fish shell?

Re: How Bash Completion Works

#28

Post by hddqsb »

jolmg wrote: post #22
nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

> 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. I've had this happen to me. Would be nice if it could be interrupted with Ctrl-C. My workaround has been to wrap the argument that's triggering that in quotes (when redoing the command in another terminal). > 2. Completion that gives me a misleading/incorrect view of the filesystem…

> Maybe a keybinding can be added to enable/disable "smart" completion (leaving only simple filepath completion). Seems like it should be a relatively quick configuration fix.

There is a keybinding to do simple filename completion: Alt-/ (https://www.gnu.org/software/bash/manual/bash.html#index-com...).

Re: How Bash Completion Works

#29

Post by earenndil »

jolmg wrote: post #22
nfoz wrote: post #12

I always disable shell completion after it burned me a few times: 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. 2. Completion that gives me a misleading/incorrect view of the filesystem, by "intelligently" filtering which files/filetypes it will let me complete. For example, if I have foo.mp3 and foo.txt, and a media-player comm…

> 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. I've had this happen to me. Would be nice if it could be interrupted with Ctrl-C. My workaround has been to wrap the argument that's triggering that in quotes (when redoing the command in another terminal). > 2. Completion that gives me a misleading/incorrect view of the filesystem…

At least in zsh, you can interrupt slow autocompletes with ^C.

Re: How Bash Completion Works

#30

Post by opk »

earenndil wrote: post #29
jolmg wrote: post #22

Earlier quoted context omitted.

> 1. Completion that blocks the shell, by doing a lookup across a network (e.g. to complete a remote path). Can hang for several seconds. I've had this happen to me. Would be nice if it could be interrupted with Ctrl-C. My workaround has been to wrap the argument that's triggering that in quotes (when redoing the command in another terminal). > 2. Completion that gives me a misleading/incorrect view of the filesystem…

At least in zsh, you can interrupt slow autocompletes with ^C.

Zsh also lets you configure, via the `remote-access` style whether you want to allow it to make remote connections for completion to begin with.
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