Simple demon bash script

The goal of this script is to allow to run simple commands as demons. Usage example to start a demon that will execute 'echo "Hello world" >> /tmp/demon.log' every 5 seconds :

./samis_demon.sh start 5 'echo "Hello world" >> /tmp/demon.log'

Usage example to stop the demon

./samis_demon.sh stop

NOTE: 1. The stop will terminate all running demons 2. In order for the demon to work it has to have read and write permissions to the directory that contains the script

#!/bin/bash
# The script allows to run a command as a demon
# Usage example to start a demon that will execute 'echo "Hello world" >> /tmp/demon.log' every 5 seconds :
# ./samis_demon.sh start 5 'echo "Hello world" >> /tmp/demon.log'
# Usage example to stop the demon
# ./samis_demon.sh stop
# NOTE:
# 1. The stop will terminate all runing demons
# 2. In order for the demon to work it has to have read and write permissions to the directory that contains the script
# @author Samuil Banti
# @copyright (C) 2018 - Samuil Banti
# @license GNU/GPLv3 http://www.gnu.org/licenses/gpl-3.0.html

demon_dir="$(cd "$(dirname "$0")" && pwd)"
demon_file=$demon_dir"/"$(basename "$0")
demon_active="$demon_dir/samis_demon_active"
action="$1"
timeout="$2"
command="$3"

# Start
if [ "$action" = 'start' ]; then
    touch $demon_active
    eval "$demon_file exec $timeout '$command' &"
    echo 'Samis demon started.'
# Stop
elif [ "$action" = 'stop' ]; then
    if [ -f "$demon_active" ]; then
        unlink $demon_active
        if [ -f "$demon_active" ]; then
            echo 'Could NOT disable the demon.'
        else
            echo 'Samis demon disabled'
        fi
    else
        echo 'No active Samis demon found.'
    fi
# Deamon
elif [ "$action" = 'exec' ]; then
    while [ -f "$demon_active" ]
    do
        eval $command
        sleep $timeout
    done
else
    echo "Usage:"
    echo "./samis_demon.sh [start|stop] [TIMEOUT] '[COMMAND]'"
fi

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