Robust Shell Script Template

script-template.sh

#!/bin/bash
#===============================================================================
#  HEADER
#==============================================================================
#  IMPLEMENTATION
#% name         bash_template
#% title		Bash Shell Template
#% version      0.0.1
#% checksum		5926ed74eb9baf0dc74b08e2e9be26a0
#% author       Matthew Myers
#% copyright	Copyright (c) http://www.metatechlabs.com
#% license      GNU General Public License
#
#===============================================================================
#  SYNOPSIS
#?   ${scriptname} [-hv] [-o[file]] args ...
#?
#? DESCRIPTION
#?    This is a script template
#?    to start any good shell script.
#?
#? OPTIONS
#?    -o [file], --output=[file]    Set log file (default=/dev/null)
#?                                  use DEFAULT keyword to autoname file
#?                                  The default value is /dev/null.
#?    -t, --timelog                 Add timestamp to log ("+%y/%m/%d@%H:%M:%S")
#?    -x, --ignorelock              Ignore if lock file exists
#?    -h, --help                    Print this help
#?    -v, --version                 Print script information
#?
#? EXAMPLES
#?    ${scriptname} -o DEFAULT arg1 arg2
#
#===============================================================================
#  OPTIONS
#  This section has several options you can select form that control the behavior
#  of the script at runtime.  DO NOT UNCOMMENT ANYTHING.  Just set the value and
#  the script parses the section below without taking up additonal memory or variables.
#
#  Option 				Validation Regexp		Description
#& outputtype=both		#(screen|logfile|both)	Send ouptput to the screen, a log file, or both.
#& errortrapping=yes	#(yes|no)				Using built-in error handling or not.
#& runlocking=no		#(yes|no)				Use RUNLOCKING to prevent multiple instances.
#===============================================================================
#  HISTORY
#@  
#===============================================================================
# END_OF_HEADER
#===============================================================================
# --- Load Properties ----------------------------------------------------------
# ----- Read only properties ---------------------------------------------------

readonly __scriptbase="$( cd $( dirname ${BASH_SOURCE[0]} ) && pwd )"
readonly __scriptname="$(basename ${0})"
readonly __this="${__scriptbase}/${__scriptname}"

# ----- Read/Write Properties --------------------------------------------------

__name=$(sed -n 's/^#%[ \t]\+name[ \t]\+//gp' "${__this}")
__title=$(sed -n 's/^#%[ \t]\+title[ \t]\+//gp' "${__this}")
__version=$(sed -n 's/^#%[ \t]\+version[ \t]\+//gp' "${__this}")
__checksum=$(sed -n 's/^#%[ \t]\+checksum[ \t]\+//gp' "${__this}")
__about=$(sed -n 's/^#% //gp' "${__this}")
__usage=$(sed -n 's/^#? //gp' "${__this}")
#__subject=od -x /dev/urandom | head -1 | awk '{OFS="-"; print $2$3,$4,$5,$6,$7$8$9}'

# --- Self Maintenance Operations ----------------------------------------------
# ----- Debugging Output -------------------------------------------------------
# A simple colorized debugging output function.  If the DEBUG environment variable
# is set then any statements using the debug function call will be output to the 
# screen with colorization via the colorized echo function defined above.
function debug() {
  declare -A color
  color=(
    [n]='\033[0m'    # Text Reset
    [k]='\033[0;30m'      # Black
    [r]='\033[0;31m'        # Red
    [g]='\033[0;32m'      # Green
    [y]='\033[0;33m'     # Yellow
    [b]='\033[0;34m'       # Blue
    [p]='\033[0;35m'     # Purple
    [c]='\033[0;36m'       # Cyan
    [w]='\033[0;37m'      # White
    [K]='\033[0;90m'      # Black
    [R]='\033[0;91m'        # Red
    [G]='\033[0;92m'      # Green
    [Y]='\033[0;93m'     # Yellow
    [B]='\033[0;94m'       # Blue
    [P]='\033[0;95m'     # Purple
    [C]='\033[0;96m'       # Cyan
    [W]='\033[0;97m'      # White
  )

  if [[ ${DEBUG} ]]
  then
    in="$*"
	out="${in//|/|\}}"
	out="${out//[/\${color[}"
	echo -e "${out}"
  fi
}

DEBUG=$(echo "${DEBUG}")
if [[ ${DEBUG} ]]; then
  echo "DEBUGGING output enabled!"
fi

# ----- Self Editing -----------------------------------------------------------

if [[ "$1" == "checksum" ]]
then
  IFS='.' read major minor rev <<< "${__version}"
  debug "Major:  ${major} Minor:  ${minor} Revision:  ${rev}"
  rev=$((rev+1))
  if [[ "${rev}" -gt 99 ]]
  then
	rev=0
	((minor++))
	if [[ "${minor}" -gt 9 ]]
	then
		((major++))
	fi
  fi
  __xx__="${major}.${minor}.${rev}"
  debug "version = ${__xx__}"

  
  cmd="sed -i" 
  script="${__this}"
  regexp="s/^\\(#%[ \\t]\\+version[ \\t]\\+\\)[0-9.]\\+/\\1${__xx__}/g"
  echo "sed -i '${regexp}' ${script}"  > "./update.sh"

  __xx__=$(md5sum "${__this}" | awk '{ print $1 }')
  debug "checksum = ${__xx__}"
  regexp="s/^\\(#%[ \\t]\\+checksum[ \\t]\\+\\)[a-zA-Z0-9]\\+/\\1${__xx__}/g"
  echo "sed -i '${regexp}' ${script}" >> "./update.sh"
  echo 'rm -f "./update.sh"' >> "./update.sh"
  .update.sh &
  exit
fi

if [[ "$1" == "name" ]]
then
  sed -i "s/^\(#%[ \t]\+name[ \t]\+\)[a-zA-Z0-9]\+/\1${__scriptname}/g" "${__this}"
fi

if [[ "$1" == "title" ]]
then
  sed -i "s/^\(#%[ \t]\+title[ \t]\+\)[a-zA-Z0-9]\+/\1$2/g" "${__this}"
fi

if [[ "$1" == "author" ]]
then
  sed -i "s/^\(#%[ \t]\+name[ \t]\+\)[a-zA-Z0-9]\+/\1$2/g" "${__this}"
fi

# ----- Self Validation --------------------------------------------------------
__xx__=$(md5sum "${__this}" | awk '{ print $1 }')
debug "Saved checksum:  ${__checksum}"
debug "Actual checksum:  ${__xx__}"

if [[ "${__checksum}" != "${__xx__}" ]]
then
	echo "The checksum for this script has changed.  If you have not modified this script recently verify the time/date stamp and the contents before running, it may be compromised."
	echo -n "Do you wish to continue with the execution of this potentialy compromised script? [Y/N] "
	read -n1 yorn
	echo
	if [[ "${yorn,,}" == "n" ]]
	then
		exit 127
	fi
fi

# - Script/Interpreter Configuration -------------------------------------------
# --- Command Interpreter Configuration ----------------------------------------

set -e				# exit immediate if an error occurs in a pipeline
set -u				#
set -o pipefail		# trace ERR through pipes
set -o errtrace		# trace ERR through 'time command' and other functions
# set -x  			# Uncomment to debug this shell script
# set -n  			# Uncomment to check your syntax, without execution.

# --- Declarations -------------------------------------------------------------
# ----- Constants --------------------------------------------------------------
readonly MINARGCOUNT=0
readonly LOGFILE="/var/log/${__scriptname}.log"

# ----- Variables --------------------------------------------------------------
declare -A color

# ----- Functions --------------------------------------------------------------

# --- Internal Features --------------------------------------------------------
# ----- Output Type Selection --------------------------------------------------
# Simple output redirection to the screen, a log file, or both all based on a simple
# setting at the top of the script.

__xx__=$(sed -ne "s/^#& outputtype=//gp" "${__this}" | sed -ne "s/#.*//gp" | xargs)
debug "outputtype = ${__xx__}"

case "${__xx__,,}" in
 'screen')
   echo "Sending all output to the screen only."
 ;;
 'logfile')
   echo "Sending all output to ${LOGFILE} only."
   exec > "${LOGFILE}"
   exec 2>&1
 ;;
 'both')
   echo "Sending all output to your screen and to ${LOGFILE}."
#   exec > "${LOGFILE}"
   exec 2>&1 | tee -a "${LOGFILE}"
 ;;
esac

# ----- Signal and Error Trapping ----------------------------------------------
# Cover trapping errors as well as a few other signals first and foremost.
__xx__=$(sed -ne "s/^#& errortrapping=//gp" "${__this}" | sed -ne "s/#.*//gp" | xargs)
debug "errortrapping = ${__xx__}"

if [[ "${__xx__,,}" == "yes" ]]
then
	trap 'echo -n "${__scriptname}: FATAL ERROR at $(date "+%HH%M") on or near line ${lineno}.\n The returned code or message was: $?." 2>&1; exit $?;' ERR INT QUIT TERM
fi
trap 'echo -n "Cleanup:  To Do"' EXIT

# ----- Locking & PID ----------------------------------------------------------

__xx__=$(sed -ne "s/^#& runlocking=//gp" "${__this}" | sed -ne "s/#.*//gp" | xargs)
__pidfile="/var/run/${__scriptname}.pid"
debug "runlocking = ${__xx__}"
debug "__pidfile = ${__pidfile}"

if [[ "${__xx__,,}" == "yes" ]]; then
  if [[ -f "${__pidfile}" ]]; then
    echo "${__scriptname} is already running"
    exit
  fi
  echo "$$" > "${__pidfile}"
fi

unset __xx__
debug "Variable __xx__ has been unset."

# --- Featured Functions -------------------------------------------------------
# ----- Featured Function Initialization ---------------------------------------
# Assign colors to a single letter color table in a global array.
function assign_colors() {
  color=(
    [n]='\033[0m'    # Text Reset
    [k]='\033[0;30m'      # Black
    [r]='\033[0;31m'        # Red
    [g]='\033[0;32m'      # Green
    [y]='\033[0;33m'     # Yellow
    [b]='\033[0;34m'       # Blue
    [p]='\033[0;35m'     # Purple
    [c]='\033[0;36m'       # Cyan
    [w]='\033[0;37m'      # White
    [K]='\033[0;90m'      # Black
    [R]='\033[0;91m'        # Red
    [G]='\033[0;92m'      # Green
    [Y]='\033[0;93m'     # Yellow
    [B]='\033[0;94m'       # Blue
    [P]='\033[0;95m'     # Purple
    [C]='\033[0;96m'       # Cyan
    [W]='\033[0;97m'      # White
  )
}

# ----- Colorized echo ---------------------------------------------------------
# Colorized echo with simplistic implementation
# Use a single letter enclosed in square brackets to indicate which color you want.
function cecho() {
  if [[ -z ${color} ]]; then assign_colors; fi
  in="$*"
  out="${in//]/]\}}"  
  out="${out//[/\${color[}"
  echo -e "${out}"
}


# --- User Segment -------------------------------------------------------------
# ----- CLI Option Processing --------------------------------------------------

if [[ $# -lt "${MINARGCOUNT}" ]] ; then
    echo "${__USAGE__}"
    exit 1;
fi

while getopts ":hAV" optname
do
 case "$optname" in
   "h")
  echo "${__USAGE__}"
  exit 0;
  ;;
   "A") 
  echo "${__ABOUT__}"
  exit 0;
  ;;
   "V")
  echo "Version ${__VERSION__}"
  exit 0;
  ;;
   "?")
  echo "Unknown option ${OPTARG}"
  exit 0;
  ;;
   ":")
  echo "No argument value for option ${OPTARG}"
  exit 0;
  ;;
   *)
  echo "Unknown error while processing options"
  exit 0;
  ;;
 esac
done

shift $(($OPTIND - 1))

# ------------------------------------------------------------------------------
#  SCRIPT LOGIC GOES HERE
# ------------------------------------------------------------------------------
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