Bash script template with usefull things

bashscript-template.sh

#!/usr/bin/env bash
#
# YOUR DESCRIPTION HERE
# 
# 
# check it with https://www.shellcheck.net/

# set -e = FAIL if any command fails
# set -o pipefail = FAIL if any command in the pipe fails
# set -u = FAIL if any variable is used, but not initialized
if test "$BASH" = "" || "$BASH" -uc "a=();true \"\${a[@]}\"" 2>/dev/null; then
    # Bash 4.4, Zsh
    set -euo pipefail
else
    # Bash 4.3 and older chokes on empty arrays with set -u.
    set -eo pipefail
fi
# expand * ALWAYS, even if in empty dirs, expand ** recursively
shopt -s nullglob globstar

# require(){ hash "$@" || exit 127; }
function require() {
    for function_to_hash in "${@}"; do
        local function_exists="$(command -v "${function_to_hash:-}" 2>/dev/null || :)"
        if [[ -z "${function_exists:-}" ]]; then
            echo "missing command ${function_to_hash:-}"; exit 1
        fi
        hash -p "${function_exists}" "${function_to_hash}"
    done
}

require 'find'
require 'grep' # etc...

# tune it for your script!
cleanup() {
    true
    #rm -f "$tmpfile"
    #...
}
trap cleanup EXIT

#####################################################
# hints
# redirect stderr to another process (stdout is dropped)
#   (my-task > /dev/null) 2> >(sed -ne '/^EMERG: /p')
# use defaults
#   var="${var:-defaultvalue}"
# how to iterate arrays
#   for f in "${my_array[@]}"; do ... done
# array length
#   ${#my_array[@]}
#####################################################

#!!!!!!!!! useful lib functions !!!!!!!!!!!!!!!!!!!!!

## Use it instead of echo!!!
println() {
    printf '%s\n' "$*"
}

# verbose exit
function die {
  >&2 echo "Fatal: ${*}"
  exit 1
}

# Split string by separator
# $1=separator $2=string
split_string(){
  array=()
  while read -rd "$1" i; do
    array+=("$i")
  done < <(printf '%s%s' "$2" "$1")
  array
}

# Print error message
err() {
  printf '%s\n' "[$(date +'%Y-%m-%dT%H:%M:%S%z')]: $*" >&2
}
#!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
#
#  More (un)useful functions
#
calc() {
  local exprs
  exprs="$1"

  echo "scale=10; ${exprs}" | bc -l
}

floor() {
  local exprs
  exprs="$1"

  printf "%.0f" "$exprs"
}


# recommended
[[ "${BASH_VERSINFO[0]}" -lt 4 ]] && die "Bash >=4 required"








# Just to remember how to do things
# 
delete_me(){ ###############################################

  while read -r f; do
    println "file=${f}"
  done < <(find /tmp)

  [[ "filename" =~ ^[[:alnum:]]+name ]] # true
  [[ "filename" == "f*" ]]              # false
  [[ "${v}" == "str" ]]                 # compare!
  [[ -z "${my_var}" ]]                  # empty? (-n = not empty)
  (( my_var > 3 )) || [[ "${my_var}" -gt 3 ]]

  (( i = 10 * j + 400 ))                # assign!

  declare -a flags
  flags=(--foo --bar='baz')             # assign array
  flags+=(--greeting="Hello ${name}")   # push into array
  readarray -t lines < <(command)       # command -> array
  for z in "${zs[@]}"; do yes; done     # iterate array
  
  local -i hundred=$(( 10 * 10 ))       # declare INT local variable
  local my_var="$(my_func)"             # !! $?=0 ALWAYS!

  tar -cf - ./* | ( cd "${DIR}" && tar -xf - )
  ret=( "${PIPESTATUS[@]}" )            # ret[0], ret[1] exit codes!
  
  # PROCESS OPTIONS
  while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do case $1 in
    -V | --version )
      echo $version
      exit
      ;;
    -s | --string )
      shift; string=$1
      ;;
    -f | --flag )
      flag=1
      ;;
  esac; shift; done
  if [[ "$1" == '--' ]]; then shift; fi

} ##########################################################
# vim: set tabstop=2:softtabstop=2:shiftwidth=2:noexpandtab