matrix.sh

#!/bin/bash

ESCAPE="\033["
WIDTH=$(tput cols)
HEIGHT=$(tput lines)

clear_screen () {
    echo -e "${ESCAPE}2J" # clear screen
    echo -e "${ESCAPE}0M" # reset styles
    echo -e "${ESCAPE}?25l" # hide cursor
}

ctrlc () {
    [[ -z "$(jobs -p)" ]] || kill $(jobs -p) # kill all subprocesses
    echo -e "${ESCAPE}2J" # clear screen
    echo -e "${ESCAPE}0M" # reset styles
    echo -e "${ESCAPE}H" # go to 0, 0
    echo -e "${ESCAPE}?25h" # show cursor
}

write_at_color () {
    # random chance of the letter being white if $4 == 255
    # aka first letter
    
    if (( $4 > 220 )) && (( RANDOM % 10 >= 9 ))
    then
        echo -e "${ESCAPE}$2;$1H${ESCAPE}97m$3"
    else
        echo -e "${ESCAPE}$2;$1H${ESCAPE}38;2;0;$4;0m$3"
    fi
}

clear_at () {
    echo -e "${ESCAPE}$2;$1H "
}

strings_fall() {
    # string coordinates
    X=$(($1))
    Y=$((RANDOM % HEIGHT))
    # string length
    LEN=$((RANDOM % 20 + 10))
    # utf-8 starting kanji
    BASE_CHAR=0x30a0
    # random delay at start
    sleep $(echo "scale=4;${RANDOM}.0/32767.0/4" | bc )
    
    while true
    do
        for (( i = 0; i < LEN; i++ ))
        do
            # new Y
            NY=$((Y - i))
            
            if (( NY < 0 ))
            then
                NY=$((NY + HEIGHT))
            fi
            # previous Y
            PY=$((NY - 1))
            
            if (( PY < 0 ))
            then
                PY=$((PY + HEIGHT))
            fi
            # seed to generate letter
            SEED=$((RANDOM % 95))
            # calculate the utf code for the letter
            CHAR=$(printf '%x\n' $((BASE_CHAR + SEED)) )
            # calculate green fading
            FADE=$((255 - 255 * i / LEN))
            # clear old char
            clear_at $X $PY
            # write new char
            write_at_color $X $NY "\u${CHAR}" $FADE
        done
        # update Y coordinate
        ((Y = (Y + 1) % HEIGHT))
        # small delay
        sleep 0.01
    done
}

# check if bc is installed
if ! [ -x "$(command -v bc)" ]; then
    echo 'Error: bc is not installed. Install it with your package manager.' >&2
    exit 1
fi

# catch SIGINT
trap ctrlc SIGINT

# clear the screen
clear_screen
# spawn string
for ((i = 0; i < WIDTH/3; i++))
do
    # they run in parallel
    strings_fall $((i * 3)) &
done
# loop forever
wait