Shell Programming and Scripting

#!/bin/bash

function on_exit {
  # evaluate statements in passed array in reverse order
  eval 'for ((i=${#'$1'[*]}-1; i>=0; i--)); do eval ${'$1'[$i]}; done'
}

function add_on_exit {
  local items_array="$1" # name of the array with statements
  shift
  eval 'local n=${#'$items_array'[*]}' # number of already existing statements in the array
  if [[ $n -eq 0 ]]; then
    eval $items_array'[$n]="unset '$items_array'"' # first unset the array (evaluated last)
    ((n++))
  fi
  eval $items_array'[$n]="$@"' # append new statement
  if [[ $n -eq 1 ]]; then # create trap, if this was the first added statement
    eval "trap 'on_exit "$items_array"' EXIT" # on_exit gets called whenever the script ends, regardless of the end-reason
  fi
}

#!/bin/bash

MUTEX=/tmp/mutex_`basename ${0}`
EXISTS=`basename ${0}`': Mutex vorhanden'
declare -a on_exit_items

source ./defineexittrapfuncs # for testing it's in the same directory

if [ -f $MUTEX ]; then
  echo -e "\n$EXISTS\n"
  exit 0
else
  date +%s > $MUTEX
  add_on_exit on_exit_items rm "$MUTEX"
  echo 'script is doing something'
fi