Question

I am trying to do a very simple bash script which emulates the behavior of checkboxes in appearance!

I want it to show some options and move the cursor to the next checkbox according to the key press of the left or right arrow keys. I’ve already managed to do this using READ and Ansii escape sequences to detect the arrow keys and I use tput to move the cursor.

My problem with this it’s that I need to read a certain letter (x for instance) to be pressed and then take another action. But how can I detect this key press and at the same time detect if an arrow key it’s being pressed or not?

To detect the ansii codes I need to read 3 characters and with the X character (the key to "select") I need to read just one, how can I read 3 characters and at the same time read just one?

Also I’ve been trying to make something so the user can JUST press the left or right arrow keys or the x key but if he presses ANY other key, nothing should happen!

I’ve done this this far:

#!/bin/bash
## Here I just print in the screen the "form" with the "checkboxes"
function screen_info(){
clear
cat <<EOF

    /\_/\_/\_/\_/\_/\_/\_/\_/\_/\_
    ||
    ||      1[ ]    2[ ]    3[ ]
    ||
    #############################



EOF
}

## This function detects the arrow keys and moves the cursor
function arrows(){

## I use ANSII escape sequences to detect the arrow keys
left_arrow=$'\x1b\x5b\x44'  #leftuierda
right_arrow=$'\x1b\x5b\x43' #rightecha
just_x_key=""

## With tput I move the cursor accordingly
cursor_x=14
cursor_y=3
tput cup $cursor_y $cursor_x

while [ -z "$just_x_key" -o "$just_x_key" != "$just_x_key" ]; do
    read -s -n3 key
    while [ `expr length "$key"` -ne 3 ]; do
        key=""
        read -s -n3 key
        break
    done
    case "$key" in
    $left_arrow)
        if [ $cursor_x -gt 14 ]; then
            cursor_x=`expr $cursor_x - 8`
        fi
        tput cup $cursor_y $cursor_x
        #This is supposed to be a simple condition detecting the x key pressed which I want to trigger something... But how to read a single character to this condition and 3 characters at the same time if the user presses the arrow key ???? =/
        #read -s just_x_key
        #if [ $just_x_key == x ]; then
        #   echo X
        #   tput cup 7 15
        #   echo "YOU PRESSED THE RIGHT KEY!!! =D"
        #fi 
        ;;
    $right_arrow)
        if [ $cursor_x -lt 28 ]; then
            cursor_x=`expr $cursor_x + 8`
        fi
        tput cup $cursor_y $cursor_x
        #read -s just_x_key
        #if [ $just_x_key == x ]; then
        #   echo X
        #   tput cup 7 15
        #   echo "YOU PRESSED THE RIGHT KEY!!! =D"
        #fi 
        ;;
    esac
done

exit $?
}


#EXECUTION
#=========

## I just call the functions!
screen_info
arrows

Yes I know, it’s not the most perfect code ever but I’m trying to learn. Suggestions will be very appreciated.

Answer 1

If you just want the checkboxes in a script, you can use the whiptail(1) or dialog(1) tools to create the checkboxes:

$ whiptail --checklist "Please pick one" 10 60 5 one one off two two off\
  three three off four four off  five five off


                 ┌──────────────────────────────────────────────────────────┐
                 │    [ ] one    one                                        │ 
                 │    [*] two    two                                        │ 
                 │    [ ] three  three                                      │ 
                 │    [*] four   four                                       │ 
                 │    [ ] five   five                                       │ 
                 │                                                          │ 
                 │              <Ok>                  <Cancel>              │ 
                 │                                                          │ 
                 └──────────────────────────────────────────────────────────┘ 

"two" "four"$ 

The final "two" "four" is the selected entries returned from the whiptail(1) program.

If you’re programming this for the fun of it yourself, let me know and I’ll just convert this to a comment in the hopes that someone else will find the hint useful in the future.