Need help on shell script option processing

Question

I am struggling to make a script have this behavior:

• I want to pass options like this ./script -ab is the same as ./script -a -b
• And have this logic: "a & b -> c", "a & c -> c", "b & c -> c" (single option is function as normal)
• Also I want this script to fall back to a function (e.g help function) when calling the script without any option

This is some example:

#!/usr/bin/env bash if [[ ${#} -eq 0 ]]; then echo "Default function" else while getopts ":a:b:c:" opt; do case ${opt} in a) echo "a" ;; b) echo "b" ;; c) echo "c" ;; *) echo -e "Invalid option: ${@}" ;; esac done fi 

Any help is appreciated

Answer 1

It's probably most straightforward to just set flags for each of the options, and then after the loop check if the flags for both A and B are set and enable C if they are.

But you could model this as a bitmap with one bit each for A and B, and C being the state where both bits are set. So A=01, B=10, C=11 plus the default state with both bits cleared. (The states correspond to default=0, A=1, B=2, C=3 in decimal or hex.) Then just set the appropriate bits when the corresponding options are seen.

Like so:

#!/usr/bin/env bash mode=0 while getopts "abc" opt; do case ${opt} in a) mode=$(( mode | 0x01 )) ;; # set rightmost bit b) mode=$(( mode | 0x02 )) ;; # set leftmost bit c) mode=$(( mode | 0x03 )) ;; # set both bits *) exit 1 ;; esac done echo "chosen mode is $mode (0 = default, 1 = a, 2 = b, 3 = c)" 

Note that you mention -A and -b in the text, but your script has a and b. getopts cares about the letter case, so those aren't the same. Also the colons in getopts a:b:c: mark the options as taking arguments, but you don't seem to need that.

Answer 2

(Edited to handle new request in the question)

You're very close. Below is the kind of thing I've done. It looks a bit complex at first, but it's a sequence of steps setting the defaults, parsing the command line, checking for bad option values or combinations, then script main routine after:

#!/usr/bin/env bash # defaults for options help=n opt_a=1 opt_b=production opt_c=0 # if no options from my user, print help message only if [[ $# -lt 1 ]]; then help=y; fi # parse command line while getopts ':ha:b:c' OPTION; do case "${OPTION}" in h) help=y ;; a) opt_a="${OPTARG}" ;; b) opt_b="${OPTARG}" ;; c) opt_c=1 ;; \?) echo "$0: Error: Invalid option: -${OPTARG}" >&2 ; exit 1 ;; :) echo "$0: Error: option -${OPTARG} requires an argument" >&2 ; exit 1 ;; esac done shift $((OPTIND - 1)) # request for help overrides other actions if [[ ${help} == 'y' ]]; then # put code here to print a USAGE message exit 0 fi # check and error out on bad options from my user # check -b: case "$opt_b" in production) ;; staging) ;; qa) ;; *) echo "$0: Error: unknown argument -b \"${opt_b}\", exiting" >&2 ; exit 1 ;; esac # script does its work starting from here 

Invoking with script-name -c -b qa will parse the options -b and -c as expected, and script-name -cb qa will also work.

I gave only one example of checking the options (to keep the answer simple); normally there would be more code to check each option and respond to legal and illegal combinations of options. I usually tuck those lines of code into a subroutine so they aren't in the middle of the script's main work flow.