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Archive for February, 2014

Basics of a Bash action game

February 24th, 2014

If you want to write an action game in bash, you need the ability to check for user input without actually waiting for it. While bash doesn’t let you poll the keyboard in a great way, it does let you wait for input for a miniscule amount of time with read -t 0.0001.

Here’s a snippet that demonstrates this by bouncing some text back and forth, and letting the user control position and color. It also sets (and unsets) the necessary terminal settings for this to look good:

#!/usr/bin/env bash

# Reset terminal on exit
trap 'tput cnorm; tput sgr0; clear' EXIT

# invisible cursor, no echo
tput civis
stty -echo

text="j/k to move, space to color"
max_x=$(($(tput cols) - ${#text}))
dir=1 x=1 y=$(($(tput lines)/2))
color=3

while sleep 0.05 # GNU specific!
do
    # move and change direction when hitting walls
    (( x == 0 || x == max_x )) && \
        ((dir *= -1))
    (( x += dir ))


    # read all the characters that have been buffered up
    while IFS= read -rs -t 0.0001 -n 1 key
    do
        [[ $key == j ]] && (( y++ ))
        [[ $key == k ]] && (( y-- ))
        [[ $key == " " ]] && color=$((color%7+1))
    done

    # batch up all terminal output for smoother action
    framebuffer=$(
        clear
        tput cup "$y" "$x"
        tput setaf "$color"
        printf "%s" "$text"
    )

    # dump to screen
    printf "%s" "$framebuffer"
done

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