Bash – How do command-line tools have their own autocomplete list

autocompletebashUbuntu

How does Bash in Ubuntu know a tool's specific list of actions?

For example if I type apt-get and tab twice I only see remove, update, upgrade …etc, but not the actions for another command or the files in the current directory.

I'm developing a command-line tool in Go and would like to provide this feature for the distros that support it.

Best Answer

It does this using bash v4's completion features. The completion code for apt-get is provided by the bash-completion package and located at /usr/share/bash-completion/completions/apt-get. Applications that have completion and are not part of the base bash-completion package place their completion scripts in /etc/bash_completion.d.

The completions are loaded via sourcing /etc/bash_completion. Exactly where this is done will vary depending on Debian or Ubuntu versions. That in turn will source everything in /usr/share/bash-completion/completions and /etc/bash_completion.d.

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Bash – How to debug and fix slow autocomplete in bash

I don't know about fixing — there are all kinds of things that could go cause delays. But I can offer a few tips to investigate.

Just as a guess, maybe there's a directory somewhere in a search path ($PATH, or some place where bash looks for completion data) that's on a filesystem which is slow to respond. Usually it's remote filesystems that are slow, but it could also be a failing hard disk, a hung FUSE driver, etc.

The first step to investigate is to run set -x to get a trace of the commands that the shell executes to generate the completions. Watch where it pauses.

If that doesn't give enough information, bring in the big guns. Note the shell's process ID (echo $$). In another terminal, run strace -f -s9999 -p$$ (or the equivalent of strace if running on another unix flavor). Strace lists the system calls performed by the process. See if it seems to be accessing files that it shouldn't, or if access to some files is slow. Adding the option -T to the strace command line makes it show the time spent in each system call.

How to enable double tab autocompletion list in csh

Try this :

in ~/.cshrc put

set filec
set autolist

Best Answer

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Bash – How to debug and fix slow autocomplete in bash

How to enable double tab autocompletion list in csh

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