source: vendor/bash/3.1-p17/examples/scripts/line-input.bash

#! /bin/bash
#
#From: kaz@cafe.net (Kaz Kylheku)
#Newsgroups: comp.unix.shell
#Subject: Funky little bash script
#Message-ID: <6mspb9$ft2@espresso.cafe.net>
#Date: Thu, 25 Jun 1998 06:11:39 GMT

#Here is something I wrote a few years ago when I was bored one day.
#Warning: this contains control characters.

# Line input routine for GNU Bourne-Again Shell
# plus terminal-control primitives.
#
# by Kaz Kylheku
# June 1996, Vancouver, Canada


#
# Function to disable canonical input processing.
# Terminal modes are saved into variable "savetty"
#
#

function raw
{
        savetty=$(stty -g)
        stty -icanon -isig -echo -echok -echonl inlcr
}

#
# Function to restore terminal settings from savetty variable
#

function restore
{
        stty $savetty
}

#
# Set terminal MIN and TIME values.
# If the input argument is a zero, set up terminal to wait for
# a keystroke indefinitely. If the argument is non-zero, set up
# an absolute timeout of that many tenths of a second. The inter-keystroke
# timer facility of the terminal driver is not exploited.
#

function settimeout
# $1 = tenths of a second
{
        if [ "$1" = "0" ] ; then
                min=1
                timeout=0
        else
                min=0
                timeout="$1"
        fi

        stty min $min time $timeout

        unset min timeout
}

#
# Input a single key using 'dd' and echo it to standard output.
# Launching an external program to get a single keystroke is a bit
# of a pig, but it's the best you can do! Maybe we could convince the
# GNU guys to make 'dd' a bash builtin.
#

function getkey
{
        eval $1="\"\$(dd bs=1 count=1 2> /dev/null)\""
}

#
# Input a line of text gracefully.
# The first argument is the name of a variable where the input line is
# to be stored. If this variable is not empty, its contents are printed
# and treated as though the user had entered them.
# The second argument gives the maximum length of the input line; if it
# is zero, the input is unlimited (bad idea).
# ^W is used to delete words
# ^R redraws the line at any time by backspacing over it and reprinting it
# ^U backspaces to the beginning
# ^H or ^? (backspace or del) delete a single character
# ^M (enter) terminates the input
# all other control keys are ignored and cause a beep when pressed
# 
#


function getline
{
        settimeout 0                    # No keystroke timeout.
        save_IFS="$IFS"                 # Save word delimiter and set it to
        IFS=""                          # to null so ${#line} works correctly.
        eval line=\${$1}                # Fetch line contents
        echo -n "$line"                 # and print the existing line.
        while [ 1 ] ; do
                getkey key              # fetch a single keystroke
                case "$key" in
                 |  )                         # BS or DEL
                        if [ ${#line} != 0 ] ; then     # if line not empty
                                echo -n " "           # print destructive BS
                                line="${line%%?}"       # chop last character
                        else                            # else if line empty
                                echo -n                # beep the terminal
                        fi
                        ;;
                 )                                     # kill to line beg
                        while [ ${#line} != 0 ] ; do    # while line not empty
                                echo -n " "           # print BS, space, BS
                                line="${line%?}"        # shorten line by 1
                        done
                        ;;
                 )                                     # redraw line
                        linesave="$line"                # save the contents
                        while [ ${#line} != 0 ] ; do    # kill to line beg
                                echo -n " "
                                line="${line%?}"
                        done
                        echo -n "$linesave"             # reprint, restore
                        line="$linesave"
                        unset linesave                  # forget temp var
                        ;;
                 )
                        while [ "${line% }" != "$line" ] && [ ${#line} != 0 ] ; do
                                echo -n " "
                                line="${line%?}"
                        done
                        while [ "${line% }" = "$line" ] && [ ${#line} != 0 ] ; do
                                echo -n " "
                                line="${line%?}"
                        done
                        ;;
                 |  |  |  |  |  |  |  |  | 
 | 
 | 
 )
                        echo -n        # ignore various control characters
                        ;;              # with an annoying beep
                 |  |  |  |  |  |  |  |  |  |  |  |  )
                        echo -n 
                        ;;
                '       ' |  | 
 | 
 |  | 
 )
                        echo -n 
                        ;;
                '' )                    # Break out of loop on carriage return.
                        echo            # Send a newline to the terminal.
                        break           # (Also triggered by NUL char!).
                        ;;
                * )             # Append character to the end of the line.
                                # If length is restricted, and the line is too
                                # long, then beep...

                        if [ "$2" != 0 ] && [ $(( ${#line} >= $2 )) = 1 ] ; then
                                echo -n 
                        else                            # Otherwise add
                                line="$line$key"        # the character.
                                echo -n "$key"          # And echo it.
                        fi
                        ;;
                esac
        done
        eval $1=\"\$line\"
        IFS="$save_IFS"
        unset line save_IFS
}

# uncomment the lines below to create a standalone test program
#
echo "Line input demo for the GNU Bourne-Again Shell."
echo "Hacked by Kaz Kylheku"
echo
echo "Use ^H/Backspace/Del to erase, ^W to kill words, ^U to kill the"
echo "whole line of input, ^R to redraw the line."
echo "Pass an argument to this program to prime the buffer contents"
raw
echo -n "go: "
if [ ${#1} != 0 ] ; then
        LINE=$1
fi
getline LINE 50
restore

echo "<$LINE>"