parse_options

#!/usr/bin/env bash
# Argument parser for --long-options
# 
# Example:
#  $ cat example
#  #!/usr/bin/env bash
#  source parse_options
#  
#  options[foo]="foo default"
#  options_flags=('verbose')
#  parse_options "$@"
#  
#  for k in "${!options[@]}"; do
#    echo "$k:${options[$k]}"
#  done
#
#  $ ./example --verbose --bar --bar-value --empty-option ''
#  verbose:on
#  bar:--bar-value
#  foo:12
#  empty-option:

declare -A options
declare -a options_flags

function parse_options {
  # Settings (from environment):
  #   options:         Associative array with defaults.
  #                    options[key]=value corresponds to:
  #                    --key value
  #
  #   options_force:   Only allow arguments already in defaults array.
  #
  #   options_flags:   Array of options that don't take a value
  #                    the value will be set to 'on'

  local arg
  local flag
  local key=''

  for arg in "$@"; do

    # Know the key, take the value
    if [[ -n $key ]]; then
      options[$key]="${arg}"
      key=''
      continue
    fi

    # Enforce the '--key value' format
    if [[ ${arg:0:2} != '--' ]]; then
      echo "[$0] Invalid argument. Name expected, got value: $arg" 1>&2
      return 1
    fi

    key="${arg:2}"

    # Is it a flag?
    for flag in "${options_flags[@]}"; do
      if [[ $flag == $key ]]; then
        options[$key]='on'
        key=''
        continue 2
      fi
    done

    # Only permit arguments defined in defaults array?
    if [[ ${options_force:0:1} == 'y' && -z ${options[$key]+_} ]]; then
      echo "[$0] Invalid option ${arg}" 1>&2;
      return 2
    fi
  done
}