Stop echo and consume all user input in Bash

Question

TARGET

Until some sub-task in script completes its job:

stop echo;
disable cursor;
consume all user input;
do not block interrupts (Ctrl+C, etc.).

WHAT HAVE DONE

For now, using this answer, I create few functions for that, here they are:

function hide_input()
{
  if [ -t 0 ]; then
    stty -echo -icanon time 0 min 0
  fi
}

function reset_input()
{
  if [ -t 0 ]; then
    stty sane
  fi
}

function stop_interactive()
{
  trap reset_input EXIT
  trap hide_input CONT
  hide_input
  tput civis
}

function start_interactive()
{
  tput cnorm
  reset_input
}

function consume_input()
{
  local line
  while read line; do line=''; done
}

And here is the way they are used:

echo "Warn the user: the job will be started."
read -p "Continue? [yes/no] > "
if [ "$REPLY" == "yes" ]; then
  stop_interactive  # <== from here all input should be rejected
  echo "Notify the user: job starting..."

  # << ------ here goes some long job with output to terminal ------>

  echo "Notify the user: job done!"
  consume_input # <== here I trying to get all user input and put nowhere
  start_interactive # <== from here restore normal operation
else
  echo "Aborted!"
  exit 0
fi

THE PROBLEM

The problem is: current 'solution' does not work. When I press keys during long running job they appears on the screen, and pressing 'Enter' ruins all output with cursor movements. Furthermore, after 'start_interactive' function call all input appears on the terminal screen.

What is the right solution for this task?

SOLUTION

Final working solution is:

function hide_input()
{
  if [ -t 0 ]; then
    stty -echo -icanon time 0 min 0
  fi
}

function reset_input()
{
  if [ -t 0 ]; then
    stty sane
  fi
}

function consume_input()
{
  local line
  while read line; do line=''; done
}

function stop_interactive()
{
  trap reset_input EXIT
  trap hide_input CONT
  hide_input
  tput civis
}

function start_interactive()
{
  consume_input
  trap - EXIT
  trap - CONT
  tput cnorm
  reset_input
}

echo "Warn the user: the job will be started."
read -p "Continue? [yes/no] > "
if [ "$REPLY" == "yes" ]; then
  stop_interactive
  echo "Notify the user: job starting..."
  do_the_job &
  pid=$!
  while ps $pid > /dev/null ; do
    consume_input
  done
  echo "Notify the user: job done!"
  start_interactive
else
  echo "Aborted!"
  exit 0
fi

Ljm Dullaart · Accepted Answer · 2017-12-23 16:04:19Z

2

Based in your question, there are many questions "why" if I look at your code. If you do not want to change the behavior of ^C etc., then don't use traps. All your functions test whether the file descriptor 0 is a terminal. Do you plan to use the script in a pipe? Also, your consuming of user input will continue until end-of-file, so the script may never end.

Based on your question, I would write something like this:

echo "Warn the user: the job will be started."
read -p "Continue? [yes/no] > "
if [ "$REPLY" == "yes" ]; then
    stty -echo
    echo "Notify the user: job starting..."
    program_to_execute &
    pid=$!
    while ps $pid > /dev/null ; do
        read -t 1 line
    done
    echo "Notify the user: job done!"
else
    echo "Aborted!"
fi
stty sane

answered Dec 23, 2017 at 16:04

Ljm Dullaart

5,0092 gold badges19 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Zlyuuka Over a year ago

it's strange, but I got a error when put 'stty -echo' to script: stty: 'standard input': Inappropriate ioctl for device when I run it from terminal all works fine, just when inside script

Zlyuuka Over a year ago

thank you for background job suggestion, it will be useful to run input consumer in main job

Zlyuuka Over a year ago

scrip will not freeze, because -icanon sets zero read timeout

Zlyuuka Over a year ago

the problem was that I piping 'yes' answer to the script!

Ljm Dullaart Over a year ago

That makes sense; [ -t 0 ] will fail and your sttys never get executed.

Collectives™ on Stack Overflow

Stop echo and consume all user input in Bash

TARGET

WHAT HAVE DONE

THE PROBLEM

SOLUTION

1 Answer 1

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

TARGET

WHAT HAVE DONE

THE PROBLEM

SOLUTION

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related