Is it possible to modify the entire line and display autocompletion suggestions in a single go in bash?

Question

Bash provides facilities to modify an entire line and change the position of the cursor with commands bound to bind -x through READLINE_LINE and READLINE_POINT variables:

$ cat test.sh
#!/bin/bash

autocompletefunc()
{
    echo $READLINE_LINE >> test.out
    READLINE_LINE='completely rewritten line & cursor is right here ->X<-'
    READLINE_POINT=51
}
$ source test.sh
$ bind -x '"\t" : autocompletefunc'
$ smth<TAB>  <== gets transformed into the below:
$ completely rewritten line & cursor is right here ->|X<-

(with | denoting the position of the cursor)

I did not find a way to modify the entire line (rather than just the currently-entered word) in an autocompletion function (registered with complete -F). Escape codes seem to just be printed (if only a single element is provided to COMPREPLY):

$ smth word<TAB>
$ smth ^[[2Kotherwisetheargumentcanentirelybereplaced

All the autocompletion variables are available "only in shell functions invoked by the programmable completion facilities". Is it possible to somehow combine the two (callback registered through complete -F and the one through bind -X) to simultaneously modify the line and list some suggestions, preferrably on <TAB><TAB>? Like this:

$ smth<TAB>
$ modified line=| further modified line
possiblevalue1
possiblevalue2
possiblevalue3

I am not sure to understand your target use case, may you elaborate? Do you expect "possiblevalueX" list is computed from "smth" so the original line before completion? — Yves Martin
– Yves Martin, Commented Aug 25, 2024 at 14:37
My use case is to "correct" the rest of the user's command (syntactically) when they ask for autocompletion for a particular parameter. Thus, I still want to present a list of suggestions, while slightly altering the surrounding parameters and perhaps the command itself. — Andriy Sultanov
– Andriy Sultanov, Commented Aug 26, 2024 at 15:58

Yves Martin · Accepted Answer · 2024-08-26 07:33:09Z

1

According to my understanding, it looks like you try to divert completion as a "command line template". The main concern with your initial proposal is to keep standard completion working when binding TAB to a function instead of standard readline command. And it seems like the builtin complete logic does not allow to replace line itself.

A work-around would be to bind TAB with a sequence of keystrokes to invoke first a function that generates line templates (here Alt-H) before standard completion (kept as Ctrl-H)

#!/usr/bin/env bash

myecho() {
    echo $*
}

_templatelines() {
    if [[ "$READLINE_LINE" == "smth" ]]; then
        READLINE_LINE='myecho  " with other parameters"'
        READLINE_POINT=7
    fi
}

_myecho_completions() {
  COMPREPLY+=("possiblevalue1")
  COMPREPLY+=("possiblevalue2")
  COMPREPLY+=("possiblevalue3")
}

complete -o nosort -F _myecho_completions myecho
bind -x '"\eH": _templatelines'
bind '"\C-H": complete'
bind '"\t":"\eH\C-H"'

Inspired from Complex keybinding in bash

Anyway, I would recommend to use a custom function and completion the standard way.

Define a smth function which runs the expected command line(s) according to some parameters when invoked
Define completion for smth function to generate expected arguments

I agree you have no option to edit template live then, but it reduce risk to impact other Bash behaviors.

edited Aug 26, 2024 at 7:33

answered Aug 26, 2024 at 7:25

Yves Martin

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2 Comments

Andriy Sultanov Over a year ago

Thank you very much for your answer! I was not able to trigger bash to list the possible completion values with your script (such as those that appear if the last three lines are commented out): ` $ myecho possiblevalue <NEWLINE> possiblevalue1 possiblevalue2 possiblevalue3 ` If "possiblevalue[1-3]" suggestion is changed to something without a common prefix, no completion is done. AFAIU, all that this script accomplishes can be done with READLINE facilities, without any autocompletion. I think it might be impossible to achieve both suggestion lists and line modification

Yves Martin Over a year ago

In my opinion, intercepting TAB prevents the double TAB sequence to display completions. I am sorry for missing the bounty

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