Bash Template

stacksofplates

I posted another version of this in another thread, but I figured I'd post a more complete version here. This template handles locking and unlocking of the script and also passing of arguments. It also includes a main function and a trap for specific signals.

#!/bin/bash

#MIT License

#Copyright (c) 2018  John Hooks

#Permission is hereby granted, free of charge, to any person obtaining a copy
#of this software and associated documentation files (the "Software"), to deal
#in the Software without restriction, including without limitation the rights
#to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
#copies of the Software, and to permit persons to whom the Software is
#furnished to do so, subject to the following conditions:

#The above copyright notice and this permission notice shall be included in all
#copies or substantial portions of the Software.

#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
#IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
#FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
#AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
#LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
#OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
#SOFTWARE.



readonly NAME=$(basename "$0")
readonly LOCKFILE=/tmp/$NAME
readonly LOCKFD=200

#Remove lock file if signal 1, 2, 3, or 6.
trap prem_end 1 2 3 6

prem_end ()
{
  echo "Premature end detected, removing lock"
  rm -rf $LOCKFILE.lock
  echo "Finished"
  exit 1
}

#Lock functions
lock () {
    local fd=${2:-$LOCKFD}
    local lockfile=$LOCKFILE.lock

    # create the lock file
    eval "exec $fd>$lockfile"

    #get the lock
    flock -n $fd && return 0 || return 1
}

unlock () {
    local fd=${2:-$LOCKFD}
    local lockfile=$LOCKFILE.lock

    #unlock
    flock -u $fd

    #remove lock file
    rm -f $lockfile
}

errexit () {
    local err="$@"

    echo $err
    exit 1
}


#Help function
function script_help () {
     echo "
         Usage: $(basename $0) [options] 
   
             -h   this help text
   
         Example:
           $(basename $0) "
   
     exit ${1:-0}
}


#Show help if no arguments or options are passed
[[ ! "$*" ]] && script_help 1
OPTIND=1


#Read command line options
#A colon after a flag means it takes an argument
#Example with extra argument called "a"
#while getopts "a:h" opt; do
#    case "$opt" in
#      a) variable=$OPTARG ;;
#      h) script_help ;;
#      \?) script_help 1 ;;
#    esac
#done
while getopts "h" opt; do
    case "$opt" in
      h) script_help ;;
      \?) script_help 1 ;;
    esac
done
shift $(($OPTIND-1));

#Main function
main () {
    lock $NAME || errexit "An instance of $NAME is still running."





    unlock
}
main