Functions for scanning command line options

Question

I know that getopts is available but I wanted to write my own as a way of improving my bash. Below I show two function definitions and an example of the use of them in a bash script. Finally I show the output of the script.

Please comment.

#!/bin/bash
# Produce a string variable which can be used by function isoption
# to give calling scripts an easy way to determine what options are
# are provided in its command line regardless of their order.  
# Call this function as:
#
#   mygetopts "$@"
#
# Non-option arguments in the command line of the caller are
# passed back to the caller in array NONOPTARGS and can be used like this:
#
#   name=NONOPTARGS[0]
#
# NOTE: Option globbing is not allowed

function mygetopts ()
{ 
# Initialize a string variable which will be made to contain all
# option names in "$@".  Since this string will be used by function
# isoption a weird variable name is used to avoid collision with
# variable names in calling script since it cannot be made local.

    O1P2T3I4O5N6="-"    # O1P2T3I4O5N6 is avaiable to caller
    declare -i i=0      # i is local to function

    if [[ "$1" == "-h" || "$1" == "--help" ]]; then
        echo "Usage: $0 \"\$@\"" >&2
        return 1
    fi

    for arg in "$@" ; do    # arg will be each positional parameter
        if [[ ${arg:0:1} == - ]]    # if $arg begins with -
            # Pack all option names separated by -
            then O1P2T3I4O5N6=${O1P2T3I4O5N6}${arg:1}-

            else NONOPTARGS[i++]=$arg
        fi
        #echo "O1P2T3I4O5N6  =$O1P2T3I4O5N6"
        #echo "NONOPTARGS = ${NONOPTARGS[@]}"
    done
    return 0
}

function isoption ()
{

    if [[ $O1P2T3I4O5N6 =~ ^.*-${1}-.*$ ]] 
        then return 0
        else return 1 
    fi
}

#!/bin/bash
# Example of using functions mygetopts and isoption to provide easy
# access to all command line options as well as non-option arguments
# regardless of their order.
#
# To use these functions place the file MYFUNCTIONS in your $HOME 
# directory and source it in your bash script before using the 
# functions.  Alternately it can be sourced by your .bash_profile

set +vx         # Change + to - to enable tracing
echo
echo These $# command line arguments are provided: 
echo "$@"

. ~/MYFUNCTIONS # source the function definitions
echo
echo These functions are defined:
compgen -A function # Show what functions are defined
echo
mygetopts "$@"  # Call mygetopts with all command line arguments

echo mygetopts returns this string with all options separated by -
echo O1P2T3I4O5N6 = $O1P2T3I4O5N6   # Show the string of all options

echo Examples of the use of isoption function:
if isoption f; then echo f found ; else echo f Not found; fi
if isoption z; then echo z found ; else echo z Not found; fi
if isoption abcd; then echo abcd found ; else echo abcd Not found; fi
if isoption abcde; then echo abcde found ; else echo abcde Not found; fi
echo
echo Examples of the accessing of non-option arguments:
inputfilename=${NONOPTARGS[0]}
outputfilename=${NONOPTARGS[1]}
echo inputfilename=$inputfilename 
echo outputfilename=$outputfilename

***13:00:47 617 ~/work>testmygetopts -bde -f infile -abcd -x outfile -y

These 7 command line arguments are provided:

-bde -f infile -abcd -x outfile -y

These functions are defined:

• isoption
• mygetopts

mygetopts returns this string with all options separated by -

O1P2T3I4O5N6 = -bde-f-abcd-x-y-

Examples of the use of isoption function:

f found
z Not found
abcd found
abcde Not found

Examples of the accessing of non-option arguments:

inputfilename=infile
outputfilename=outfile

Answer 1

The bash code all looks reasonably fine to me.

The -h and --help output doesn't look right (it will print the actual parameters passed, but should print the list of allowable options/parameters?)

Options like --this-will-break won't work with --will or --break.

I'm not clear if parameters with spaces in them will work, as in: testmygetopts "this is one argument"

I think 'isoption' could be simplifed to just be the [[ ]] expression (since it will return 0 or 1 already).

Answer 2

…

declare -i i=0      # i is local to function

Inside a function declare and local do the same thing, but if you're going to write a code comment saying it's local, don't you think the local keyword is more self-documenting? I'd write it…

local -i i=0

if [[ "$1" == "-h" || "$1" == "--help" ]]; then

…

This is fine, but you don't actually need double quotes inside a double-bracket test. You don't need the double-equals either. That's up to you.

echo "Usage: $0 \"\$@\"" >&2

Use printf and single quotes for better readability. You immediately know the "$@" won't expand in single quotes, and the "$0" gets expanded before printf interpolates it.

printf 'Usage: %s "$@"\n' "$0" >&2

…

for arg in "$@" ; do    # arg will be each positional parameter

Same as for arg without the in "$@" part. Up to you.

if [[ ${arg:0:1} == - ]]    # if $arg begins with -

More efficiently written:

if [[ $arg = -* ]]

…

function isoption ()
{

    if [[ $O1P2T3I4O5N6 =~ ^.*-${1}-.*$ ]] 
        then return 0
        else return 1 
    fi
}

A nice bash feature is that return always returns the value of $?, so you could write this:

[[ $O1P2T3I4O5N6 =~ ^.*-${1}-.*$ ]]
return

But if you prefer explicit, your code is fine.

---

On to the example part:

echo
echo These $# command line arguments are provided: 
echo "$@"

This use of echo is the only thing I think it actually wrong. Echo takes options (-neE), so you should never give it an unsanitized "$@" to output. Use printf here.

printf '%s ' "$@"; echo

And the rest is fine. Very nice job!