forever.sh - should keep a process alive forever

Question

This script's only responsibility is to keep a process alive. Forever. It's sole dependencies shall be bash and coreutils. I'm not sure if it would be compatible with sh, that would be even better.

#!/bin/bash
#
# (c) Netcetera AG
# Author:  Christian Mäder
date="10.07.2015"
version="1.0"
#

respawn() {
    while true; do
        $myprocess
        exit_code=$?

        now=`date +"%Y-%m-%dT%H:%M:%S%z"`

        if [ $exit_code -ne 0 ] || [ $force -eq 1 ]; then
            if [ $quite -eq 0 ]; then
                echo "$now | service $myprocess crashed with code $?. Restarting after ${timeout}s." >&2
            fi
            sleep $timeout
        else
            break
        fi
    done
}

help() {
    echo "Usage: $1 [-f] [-q] [-t #] \"command\""
    echo "       $1 -v"
    echo "       $1 -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 runnig forever."
    echo "Version $version from $date."
}

while true; do
    case "$1" in
        "--help")
            help $0
            break
            ;;
        "-h")
            help $0
            break
            ;;
        "-v")
            about
            break
            ;;
        "-q")
            quite=1
            shift
            ;;
        "-f")
            force=1
            shift
            ;;
        "-t")
            if [[ $2 =~ '^[0-9]+$' ]]; then
                timeout=$2
                shift
            fi
            shift
            ;;
        *)
            if [ $# -eq 0 ]; then
                about
                echo
                help $0
            else
                quite=${quite-0}
                force=${force-0}
                timeout=${timeout-"1"}
                myprocess=$1
                respawn
            fi
            break
            ;;
    esac
done

---

For everyone's reference have I created a gist with an updated version which incorporated the feedback.

Answer 1

By quite, you mean quiet, I think. You also have a typo with "runnig".

The script would be better self-documented if you put the about and help functions first.

In help, instead of echoing $1, which may be a path, it would be more conventional to echo just the basename.

It would be more elegant for the respawn function to accept the command as a parameter rather than using the $myprocess global variable. "Process", to me, implies a particular instance, i.e. a running program with a PID, so I'd rename myprocess to command. You only need to execute date if you're actually going to print a log message. I'd rearrange the conditions to emphasize how to exit the loop and to reduce nesting.

respawn() {
    command="$1"
    while true; do
        $command
        exit_code=$?

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

---

In the argument parser, the --help and the -h conditions are identical. You should write

case "$1" in
    "--help"|"-h")
        help "$0"
        break
        …

Note that double-quoting variables is a good habit.

I don't believe that the [[ $2 =~ '^[0-9]+$' ]] test is available in traditional Bourne shell. If portability is a concern, you could write the not-quite-equivalent test

case "$2" in
    [0-9]*) timeout=$2 ; shift
    ;;
esac
shift

Answer 2

Some things that ShellCheck spotted:

now=`date +"%Y-%m-%dT%H:%M:%S%z"`
    ^--- use $(...) instead of legacy `...`

if [ $exit_code -ne 0 ] || [ $force -eq 1 ]; then
                             ^--- use "$force" to prevent globbing
                                  and word splitting

(Note that no quoting of $exit_code is needed since it was assigned from $?.)

if [ $quite -eq 0 ]; then
     ^--- use double quotes  (should this be $quiet ?)

sleep $timeout
      ^--- use double quotes

help $0
     ^--- use "$0"  (3 different places)

if [[ $2 =~ '^[0-9]+$' ]]; then
            ^--- Don't quote rhs of =~, it'll match
                 literally rather than as a regex.