Wait for a Key press on a Shell Script

Question

I made a Bourne shell script, and I need to improve it by adding a "Press Esc button to execute a command".

This is a working example in BASH :

#!/bin/bash
read -s -n1 key
case $key in
$'\e') echo "escape pressed";;
*) echo "something else" ;;
esac

But I couldn't make it work in Bourne shell — Error : "read: Illegal option -s"

Can you please help me find a Bourne shell solution because almost all the information on Google is about Bash statements.

Answer 1

According to our exchanges in comments, your specific question, and the question on Unix & Linux Stack Exchange Can I read a single character from stdin in POSIX shell?, this is a complete solution:

#!/bin/sh

set -eu

# usage: readc <variable-name>
readc()
{
    if [ -t 0 ]
    then
        # if stdin is a tty device, put it out of icanon, set min and
        # time to sane value, but don't otherwise touch other input or
        # or local settings (echo, isig, icrnl...). Take a backup of the
        # previous settings beforehand.
        saved_tty_settings=$(stty -g)
        stty -echo -icanon min 1 time 0
    fi
    eval "$1="
    while
        # read one byte, using a work around for the fact that command
        # substitution strips trailing newline characters.
        c=$(dd bs=1 count=1 2> /dev/null; echo .)
        c=${c%.}

        # break out of the loop on empty input (eof) or if a full character
        # has been accumulated in the output variable (using "wc -m" to count
        # the number of characters).
        [ -n "$c" ] &&
            eval "$1=\${$1}"'$c
        [ "$(($(printf %s "${'"$1"'}" | wc -m)))" -eq 0 ]'; do
        continue
    done
    if [ -t 0 ]
    then
        # restore settings saved earlier if stdin is a tty device.
        stty "$saved_tty_settings"
    fi
}

# Reads one character.
readc key

# Acts according to what has been pressed.
case "$key" in
  "$(printf '%b' '\033')") echo "escape pressed";;
  *) echo "something else" ;;
esac