forever.sh

#!/bin/bash
#
# (c) Netcetera AG

date="19.11.2015"
version="1.2"
#

help() {
    script=$(basename "$1")
    echo "Usage: $script [-f] [-q] [-t #] \"command\""
    echo "       $script -v"
    echo "       $script -h"
    echo
    echo "  -v             : Shows the version of this tool."
    echo "  -h             : Shows this help text."
    echo "  -f             : Restart the program even if it exited with an exit"
    echo "                   status of 0."
    echo "  -q             : If set, this script won't write anything to stdout or stderr."
    echo "  -t #           : Seconds for how long the script should wait until"
    echo "                   the restart happend."
    echo "  command        : The command to execute continuously until it exits"
    echo "                   gracefully or forever if -f is set."
    echo
    echo "Example: $1 -f -t 2 \"echo hello, see you again in two.\"" 
}

about() {
    echo "Respawns a process which dies. Hence it keeps it running forever."
    echo "Version $version from $date."
}

respawn() {
    command="$@"
    while :; do
        $command
        exit_code=$?
        
        if [ $exit_code -eq 0 ] && [ "$force" -ne 1 ]; then
            break
        elif [ "$quiet" -eq 0 ]; then
                echo "$(date +\"%Y-%m-%dT%H:%M:%S%z\") | service $command crashed with code $?. Restarting after ${timeout}s." >&2
        fi
        sleep "$timeout"
    done
}

while true; do
    case "$1" in
        "--help"|"-h")
            help "$0"
            break
            ;;
        "-v")
            about
            break
            ;;
        "-q")
            quiet=1
            shift
            ;;
        "-f")
            force=1
            shift
            ;;
        "-t")
            case "$2" in
                [0-9]*)
                    timeout=$2
                    shift
                    ;;
                *)
                    echo "The parameter for -t must be a positive number, but was '$2'."
                    help "$0"
                    break
                    ;;
            esac
            shift
            ;;
        *)
            if [ $# -eq 0 ]; then
                about
                echo
                help "$0"
            else
                quiet=${quiet-0}
                force=${force-0}
                timeout=${timeout-"1"}
                respawn "$@"
            fi
            break
            ;;
    esac
done