bash command line util template

command_line_template.sh

#!/bin/bash
# create a place holder for positional args
POS_ARGS=""

while (( "$#" )); do #while there are still args to parse
  # look at the first one
  case "$1" in
    # this is an example of a boolean flag.
    -a|--my-boolean-flag)
      # If present do something with MY_FLAG
      MY_FLAG=0
      # drop the first argument
      shift
      ;;
    # this is an example of a flag with an argument
    -b|--my-flag-with-argument)
      # check that there is an argument ($2) and that it does not start with '-'
      if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then
        # set MY_FLAG_ARG to $2
        MY_FLAG_ARG=$2
        # drop the first two arguments
        shift 2
      else
        # output an error msg, (> &2 redirects to stderr)
        echo "Error: Argument for $1 is missing" >&2
        exit 1
      fi
      ;;
    -*) # unsupported flags
      # started with -*|--*=) but the second part seems unnecessary
      # output an error msg, (> &2 redirects to stderr)
      echo "Error: Unsupported flag $1" >&2
      exit 1
      ;;
    *) # preserve positional arguments
      POS_ARGS="$POS_ARGS $1"
      shift
      ;;
  esac
done
# set positional arguments in their proper place -> $1 $2 ...
eval set -- "$POS_ARGS"

echo "my flag is $MY_FLAG"
echo "my flag arg=$MY_FLAG_ARG"
echo $POS_ARGS