Command to inject string into command line, like a pre-filled command to edit before execution

Question

With $ as my bash prompt and ⏎ symbolizing me hitting the enter key in the following example, how could I construct a command/alias foo so that

$ foo bar⏎

would enter/input/pre-fill/type "bar" (or any other string I pass to the command) to the command line, so that I can modify "bar" before hitting Enter? E.g.

$ bar
…
$ barbaz⏎ 

I've unsuccessfully tried echo bar > /dev/pts/123 and would like to do without xdotool. Is this possible?

---

EDIT: Example use case, a "greppy autocomplete":

I often need long commands with many arguments that are hard to remember. I keep examples in a file:

commands.txt:

ffmpeg -i infile.mp4 -c:v copy -c:a copy -y transcoded.mp4
sox in.wav out.wav remix 1 0

now, if I had the command as specified above, let's call it inject, I could have an alias

grepcomplete () {
  inject $(grep $0 commands.txt)
}

so when I remember that I need to remix something, but I don't remember sox and its arguments, I can type grepcomplete remix, and then have sox in.wav out.wav remix 1 0 sit on my command line, as if I typed it out, ready for me to edit and adapt, before I execute it by hitting enter. Without the need to select, copy, paste anything.

As Kamil suggests in the comments, I could use bash's history search (Ctrl-R), and provide my own "history" by doing something like history -r commands.txt in my bashrc.
Still, my approach has the benefit that I can easily hack it, e.g. by displaying all matches with syntax highlighting.

Please note that I've answered this question myself, where I provide an implementation of this inject command.

Answer 1

Here's a small and ugly solution, inspired by a perl solution to insert a string after each prompt, using TIOCSTI adapted to python:

A bash function, e.g. for .bashrc

inject () {
(python -c "import fcntl; import termios; import sys
with open('/dev/stdout', 'w') as fd:
  for c in ' '.join(sys.argv[1:]): fcntl.ioctl(fd, termios.TIOCSTI, c)" "$@" &)
}

Usage:

inject foo bar

Notes:

• can't handle Unicode at the moment! I suspect the for char in str is to blame?
• The background-in-subshell construct ( foo &) prevents double-echo'ing the string before the prompt
• It will eat whitespace between arguments: inject foo bar = inject foo bar. Use inject "foo bar".
• It looks like it depends on timing, so race conditions might arise?
• I had other versions with Python's threads/multiprocessing that can do without the bash subshell and might work better for piping, xargs etc. This was the cleanest and simplest solution for my use case.

Answer 2

You can configure this using ~/.inputrc. Create the file if it doesn't exist, and add this:

Control-P: "foo "

Now, open a new terminal and press Ctrl+P and the string foo will be entered where your cursor is. You can choose a shortcut that works for you, and it should work.

Answer 3

xdotool will only work in X environment, and won't work in the TTY shell and may not work in Wayland.

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I feel like you are asking about creating your own bash completion script. Then, "inject" (invoke the completion) with Tab key.

The basic idea is this complete command which says to bash what to suggest when user hits Tab key:

$ complete -W "now tomorrow never" dothis

Then, typing

$ dothis to<Tab>

fills it:

$ dothis tomorrow

For your example,

$ complete -W bar foo
$ foo<Space><Tab>

will produce

$ foo bar

Which you can edit futher.

The complete command itself could be placed into ~/.bashrc to be run during interactive shell creation.

Answer 4

If switching to zsh is an option, then it's just:

print -rz -- "$text"

To seed zsh's line editor (zle) with the given text.

If done within a custom zle widget, you'd do:

LBUFFER+=$text

to insert the text at the cursor, or:

BUFFER+=$text

To insert at the end, or:

BUFFER[n,0]=$text

To insert it before the n^th character in the editing buffer.

So

BUFFER[CURSOR+1,0]=$text

Would insert the text at the cursor without moving the cursor position, same as:

RBUFFER[1,0]=$text

With:

• $BUFFER: full editing buffer
• $CURSOR: current cursor position inside that buffer (0 at the start)
• $LBUFFER/$RBUFFER: for convenience the portion of $BUFFER left and right of the cursor respectively.

See info zsh widgets for details.

Answer 5

In fish the equivalent is using the commandline function. For example:

commandline 'echo next command'