A template bash script based on google style guide with some little improvements

bash-template

#!/bin/bash

# Here short description of this script
# This is just a template to be used for writing new bash scripts

###
# Above all else, for the script utilities and applications you create aspire to:
# * Write small utilities with a singular focus, a limited scope, just one job.  Do that job well.
# * Write utilities that are flexibile on how input is provided (e.g. pipes, redirection, ...)
# * Build application by composing these utilities or functions.
##

###
# Based on Google Style Guide: https://google.github.io/styleguide/shell.xml
# General remarks
# * Executables should have no extension (strongly preferred) or a .sh extension. 
# * Libraries must have a .sh extension and should not be executable
# * SUID and SGID are forbidden on shell scripts. 
# * ~All error messages should go to STDERR.~ Any output that not part of the utilities
# * Write todos like this: # TODO(renzok): Handle the unlikely edge cases (bug ####)
# * Indent 2 spaces. No tabs. 80 chars max per line
# * Put `; do` and `; then` on the same line as the `while`, `for`, or `if` statement. 
# * Quoting: https://google.github.io/styleguide/shell.xml#Quoting
# * ~Function Names: Lower-case, with underscores to separate words.~
# * Module level variable names are all caps.
# * Function scoped variables are lower case and use the `local` keyword.
# * Function names: lower-case with hypens or underscores.  Just be consistent within a utility/library/application.
# ** Separate libraries with ::. Parentheses are required after the function name. 
# * prefer shell builtin over separate process
##


##
# Coding tips and tricks:
# http://stackoverflow.com/questions/1167746/how-to-assign-a-heredoc-value-to-a-variable-in-bash
#

# Exit immediately if a command exits with a non-zero status.
#
# This might cause problems e.g. using read to read a heredoc cause
# read to always return non-zero set -o errexit Treat unset variables
# as an error when substituting.
set -o nounset

# 1. section: global constants (all words upper case separated by underscore)
# declare -r CONSTANT_VARIABLE='value'
declare -r TMP_FILE_PREFIX=${TMPDIR:-/tmp}/prog.$$

# as per discussion
# http://stackoverflow.com/questions/4774054/reliable-way-for-a-bash-script-to-get-the-full-path-to-itself
# but use BASH_SOURCE[0]
declare -r SCRIPTPATH=$( cd $(dirname ${BASH_SOURCE[0]}) > /dev/null; pwd -P )


# 2. section: functions
# Part of a package/library
function mypackage::my_func() {
 
}

function _check_required_programs() {

    # Required program(s)
    req_progs=(readlink xmllint xsltproc curl date sed)
    for p in ${req_progs[@]}; do
	hash "${p}" 2>&- || \
	    { echo >&2 " Required program \"${p}\" not installed or in search PATH."; 
              exit 1; 
            }
    done
    
}
function cleanup() {
    rm -f ${TMP_FILE_PREFIX}.*
    
    echo "always implement this" && exit 100   
}


function usage() {
  cat <<EOF

Usage: $0

 TODO
EOF
}


# Single function
function main() {

  # the optional parameters string starting with ':' for silent errors snd h for help usage
  local -r OPTS=':h'

  while builtin getopts ${OPTS} opt "${@}"; do
      
      case $opt in
	  h) usage ; exit 0
	     ;;
	  
	  \?)
	      echo ${opt} ${OPTIND} 'is an invalid option' >&2;
	      usage;
	      exit ${INVALID_OPTION}
	      ;;
	  
          :)
	      echo 'required argument not found for option -'${OPTARG} >&2;
	      usage;
	      exit ${INVALID_OPTION}
	      ;;
          *) echo "Too many options. Can not happen actually :)"
             ;;
 	  
      esac
  done
  

  cleanup

  exit 0
}


# Always check return values and give informative return values. 
# see https://google.github.io/styleguide/shell.xml#Checking_Return_Values

# set a trap for (calling) cleanup all stuff before process
# termination by SIGHUBs
trap "cleanup; exit 1" 1 2 3 13 15
# this is the main executable function at end of script
main "$@"