Shell script to begin or end a spinner background process

spin.sh

#!/bin/sh

help() {
    cat << EOF
spin(1)

NAME
    spin - begin or end a spinner background process

SYNOPSIS
    spin [-m message] [-b begin] [-e end (PID)] [-h help]

OPTIONS
    -m  message
        Spinner message.

    -b  begin
        Begins a spinner as a background process.    

    -e  end (PID)
        Ends a spinner process by PID.

    -s  speed
        Optional replacement spinner speed in seconds. Default is '0.25'.

    -c  characters
        Optional replacement characters. Example '-\|/'. Default is '⠈⠁⠈⠑⠈⠱⠈⡱⢀⡱⢄⡱⢄⡱⢆⡱⢎⡱⢎⡰⢎⡠⢎⡀⢎⠁⠎⠁⠊⠁'.

    -i  increment
        Optional replacement character increment. Example '1'. Default is '2' (the default braile characters are grouped by two).

    -f  file
        Optional replacement file location for storing the spinner process PID. Default is '$HOME/spin.pid'

    -h  help
        Prints this help message.
EOF
}

begin() {
    local MESSAGE=$1
    local SPEED=$2
    local CHARACTERS=$3
    local INCREMENT=$4
    
    i=0;
    while true; do 
        printf "\r${CHARACTERS:i%${#CHARACTERS}:$INCREMENT} $MESSAGE"; i=$((i+INCREMENT)); sleep $SPEED
    done    
}

end() {
    local PID=$1
    local FINISHED=' ✓'
    local MESSAGE=$2
    printf "\r\033[K$FINISHED $MESSAGE\n"
    kill $PID
}

while getopts 'hbe:m:s:c:i:f:' OPTION; do
    case $OPTION in
        m) export MESSAGE="${OPTARG}" ;;
        b) BEGIN=1 ;;
        e) PID="${OPTARG}" ;;
        s) SPEED="${OPTARG}" ;;
        c) CHARACTERS="${OPTARG}" ;;
        i) INCREMENT="${OPTARG}" ;;
        f) FILE="${OPTARG}" ;;
        h) help; exit 0 ;;
        *) echo Invalid arg; exit 1 ;;
    esac
done

shift $(($OPTIND - 1))

if ([ -n "${BEGIN}" ] || [ -n "${PID}" ]) && [ -z "${MESSAGE}" ]; then
    echo "-m (message) must be included when -b (begin) or -e (end) are specified." >&2
    exit 1
fi

if [ $BEGIN ]; then
    DEFAULT_SPEED='0.25'
    DEFAULT_CHARACTERS='⠈⠁⠈⠑⠈⠱⠈⡱⢀⡱⢄⡱⢄⡱⢆⡱⢎⡱⢎⡰⢎⡠⢎⡀⢎⠁⠎⠁⠊⠁'
    DEFAULT_INCREMENT='2'
    DEFAULT_FILE="${HOME}/spin.pid"

    begin "${MESSAGE:-}" ${SPEED:-$DEFAULT_SPEED} "${CHARACTERS:-$DEFAULT_CHARACTERS}" ${INCREMENT:-$DEFAULT_INCREMENT} &
    PID=$!
    echo $PID > ${FILE:-$DEFAULT_FILE}
elif [ $PID ]; then
    end $PID "$MESSAGE"
fi

spin_test.sh

#!/bin/sh

# Set replacement values.
BEGIN_MESSAGE="Testing 😬"
SPEED='0.1'
CHARACTERS='-\|/'
INCREMENT='1'
END_MESSAGE="Tested 👍"
FILE=`mktemp`

./spin.sh -b -m "$BEGIN_MESSAGE" -s $SPEED -c $CHARACTERS -i $INCREMENT -f $FILE
for i in {1..5}; do sleep 1; done
PID=`cat $FILE`
./spin.sh -e $PID -m "$END_MESSAGE"

# Cleanup.
rm $FILE

# Check cleanup.
ps | grep -v grep | grep --quiet "$PID"
[ "$?" = 0 ] && echo $PID was still running 👎 && kill $PID && exit 1 || echo ' ✓' PID $PID correctly killed 👍
ls $FILE >/dev/null 2>&1
[ "$?" = 0 ] && echo $FILE was still present 👎 && rm $FILE && exit 1 || echo ' ✓' Temp file $FILE correctly removed 👍