parsOpts.sh 
Description: parsOpts is bash shell function that can be used by bash scripts to parse positional parameters into options 
and corresponding arguments 
Author: Andrew T. Withers (atw31337@gmail.com) 

# Basic usage: 

source /path/to/file/parsOpts.sh 

while [[ $OPTIND -lt $# ]]; do
	parsOpts "$@" "a:,b,c::,d:3,help,e:0,f:1,g"
	case $OPT in
	a)
		commands
		;;
	b)
		commands
		;;
	c)
		commands
		;;
	d)
		commands
		;;
	help)
		usage
		exit
		;;
	e)
		commands
		;;
	f)
		commands
		;;
	g)
		commands
		;;
	:)
		echo "Invalid number of arguments for option $OPTARG. $OPTARG requires $NUMARGS argument(s)."
		exit1
		;;
	\?)
		echo "Invalid option: $OPTARG"
		exit 1
		;;
	esac 
done 
shift "$OPTIND"

	parsOpts is a bash function. The code can either be copied directly into the head of the script or it can be saved as a 
separate file and linked to the script using the source command. 

	parsOpts requires two parameters when it is called. The first "$@", is a reserved variable, created by the shell, that
contains all of the positional parameters that are passed to the script. The second is the optstring. The optstring tells 
parsOpts which options are possible and the number of arguments that each one requires. parsOpts can parse three different 
types of options: Short options, long options, and stringed short options. Short options are a single option denoted by the 
prefix '-' and a letter (ex: -a). Stringed short options are several short options that are strung together into a single 
parameter (ex: -abcd). This example shows four short options being passed together and is equivalent to -a -b -c -d. Long options 
consist of entire words and are denoted by the prefix '--' (ex: --help). Each of these types of options may also have a single 
argument, no arguments, a specific number of arguments, or an unknown number of arguments. This is determined by the optstring. 

# Optstring format 

Example: 
"a,b:,c::,d:0,e:1,f:3,help,long:,option::,count:2" 

	All options in the optstring are comma-separated and the entire string is enclosed in double quotes. The number of 
arguments required by each option is determined by what follows the option. An option with no colon is interpreted as having 
no arguments. A single colon ':' is interpreted as an option requiring one argument. A double colon "::" represents an unknown 
number of arguments. An option followed by a colon and a number ':2' denotes a specific number of arguments. The example 
demonstrates that no arguments and one argument can also be defined using the latter formatting scheme ("d:0,e:1"). When an 
option is defined as having an unknown number of options, parsOpts will continue to associate arguments with that option until 
either another option is found or all the parameters have been parsed; therefore, if non-option arguments are required, an 
option with an unknown number of arguments cannot be the last option passed. Otherwise, the non-option argument(s) will be 
associated with this option. (Ex: -a This is an example non-option). The non-option argument was not intended to be associated 
with -a; however, because -a was defined in the optstring as "a::" parsOpts cannot distinguish this. It is recommended to use a 
defined number of arguments whenever possible. 
	parsOpts will continue to parse options and their arguments until a non-option argument, as defined by optstring, is 
found. The global variable OPTIND tracks which parameter is to be parsed next. OPTIND starts at 0; therefore, the parameter 
at $1 is at OPTIND 0. If the first option has 3 arguments, OPTIND will be 4 after the first iteration. The option itself is at 
index 0 in addition to 3 args. OPTIND 4, $5, is the next parameter to be processed. If that parameter begins with '-' or '--' 
it is then parsed as an option. Otherwise, parsOpts will not continue. shift "$OPTIND" can be used after the while loop in 
order to shift the positional parameters to the first non-option argument. In the previous example, this would shift $5 to $1. 

# Stringed short option arguments 

	Each of the options in a stringed short option are processed individually; therefore, they share the same set of 
arguments, the parameters that follow the stringed option. Each of the options in the string can require a different number of 
arguments. Each of them will associate with the first n number of parameters. A global variable, 
____Stringed_Short_Option_Highest_Arg_Count is used to track which of the options in the string required the highest number of 
arguments. parsOpts then increments OPTIND this many parameters after all of the options in the string have been processed. 

# Global variables 

OPTIND - Maintains the index number of the next parameter to be processed. 
OPT - The option name. If not enough arguments were present for an option, the value of OPT is set to ':'. If the option is not 
	defined in the optstring, the value of OPT is set to '?'. 
OPTARG - The argument(s) for the OPT in a space separated string. If not enough arguents were present for an option 
	or the option was not defined in optstring, the value of OPTARG is set to the name of the option. 
NUMARGS - Contains the number of expected arguments for OPT in the instance that not enough arguments were present. 
____Stringed_Short_Index - a global variable that stores the index number of the next option to be processed in a stringed
	short option.
____Stringed_Short_Option_Highest_Arg_Count - a global variable that keeps track of the highest number of arguments required 
	for options in a stringed short option. 
  
* The stringed short option global variables are simply used to track certain data between iterations. They are not intended 
	to be used by the script itself and any manipulation of these variables may have unexpected consequences.

Feel free to contact me, at the email address above, if you have any questions or feedback, or if you encounter any issues.