Bash – Echo text as suggested prompt in bash

bashline-editor

Is it possible to change text that appears after $PS1. It is what user inputs. I want to suggest some command hereafter my_function is run. Of Course I should be able to modify/delete it using backspace key

root@linux: 
root@linux: ls
aplha beta gamma
root@linux: my_function
root@linux: echo_something_here (It should be deletable by me)

Best Answer

Based on this answer you can use expect (you might have to install it first):

#!/usr/bin/expect -f

# Get a Bash shell
spawn -noecho bash

# Wait for a prompt (in my case was '$', but your example only put ':')
expect ": "

# store the first argument in a variable
set arg1 [lindex $argv 0]

# Type something
send $arg1

# Hand over control to the user
interact

exit

Now you can call it (assuming you saved it as my_function):

root@linux: ./my_function "some text here"
root@linux: some text here

The only undesirable effect might be that it starts a new bash.

Related Solutions

Bash – Can Bash Write to Its Own Input Stream?

With zsh, you can use print -z to place some text into the line editor buffer for the next prompt:

print -z echo test

would prime the line editor with echo test which you can edit at the next prompt.

I don't think bash has a similar feature, however on many systems, you can prime the terminal device input buffer with the TIOCSTI ioctl():

perl -e 'require "sys/ioctl.ph"; ioctl(STDIN, &TIOCSTI, $_)
  for split "", join " ", @ARGV' echo test

Would insert echo test into the terminal device input buffer, as if received from the terminal.

A more portable variation on @mike's Terminology approach and that doesn't sacrifice security would be to send the terminal emulator a fairly standard query status report escape sequence: <ESC>[5n which terminals invariably reply (so as input) as <ESC>[0n and bind that to the string you want to insert:

bind '"\e[0n": "echo test"'; printf '\e[5n'

If within GNU screen, you can also do:

screen -X stuff 'echo test'

Now, except for the TIOCSTI ioctl approach, we're asking the terminal emulator to send us some string as if typed. If that string comes before readline (bash's line editor) has disabled terminal local echo, then that string will be displayed not at the shell prompt, messing up the display slightly.

To work around that, you could either delay the sending of the request to the terminal slightly to make sure the response arrives when the echo has been disabled by readline.

bind '"\e[0n": "echo test"'; ((sleep 0.05;  printf '\e[5n') &)

(here assuming your sleep supports sub-second resolution).

Ideally you'd want to do something like:

bind '"\e[0n": "echo test"'
stty -echo
printf '\e[5n'
wait-until-the-response-arrives
stty echo

However bash (contrary to zsh) doesn't have support for such a wait-until-the-response-arrives that doesn't read the response.

However it has a has-the-response-arrived-yet feature with read -t0:

bind '"\e[0n": "echo test"'
saved_settings=$(stty -g)
stty -echo -icanon min 1 time 0
printf '\e[5n'
until read -t0; do
  sleep 0.02
done
stty "$saved_settings"

PID files which I'm not familiar with, but I would suggest using pgrep as workaround.
ds4drv seems a daemon but udev supports only short running processes.

RUN{type}

...

This can only be used for very short-running foreground tasks. Running an event process for a long period of time may block all further events for this or a dependent device.

Starting daemons or other long-running processes is not appropriate for udev; the forked processes, detached or not, will be unconditionally killed after the event handling has finished.

Make a copy of that script:

#!/bin/bash
# DS4 Check Script

pgrep ds4drv || ds4drv --hidraw --config /home/user/.config/ds4drv.conf & disown

Best Answer

Related Solutions

Bash – Can Bash Write to Its Own Input Stream?

Further reading

Bash – Improving the Bash script

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