Remove options from command

Question

My inputs are commands followed by an unrestricted number of single-letter options, e.g. command -abc. Neither the command nor the options take any arguments. My goal is to remove certain options.

Removing options b and c as an example, I can achieve this like this:

$ cmd='command -abc'
$ pattern='(.*) -(.*)'
$ [[ $cmd =~ $pattern ]]
$ echo "${BASH_REMATCH[1]} -${BASH_REMATCH[2]//[cb]}"
command -a

However, this only works in bash. How can I solve this problem in a compatible way, e.g. using sed and grep ?

What is known about the command? Do you know all its options and what options takes arguments? — Kusalananda
– Kusalananda ♦, Commented Oct 17, 2022 at 19:35
Another way to put it: In your example, command -abc, how do you know it isn't a single option -a with an option-argument bc (or -a -b c, i.e. -b takes an option-argument)? And what happens with command -abc -d -- -abc? With real command line parsing, removing -b and -c, that should probably become command -a -d -- -abc, assuming -a takes no argument, and regardless of whether -b takes an argument or not, right? If -a takes an argument, the command line options should remain unchanged, right? — Kusalananda
– Kusalananda ♦, Commented Oct 17, 2022 at 20:06
@Kusalananda there are no arguments/option-arguments for the command, only single-letter options. In case there are no options the input is command --. — rewire
– rewire, Commented Oct 18, 2022 at 6:56

Kusalananda · Accepted Answer · 2022-10-18 10:01:14Z

Assuming that the command only takes single letter options, and that none of the options takes an argument, we may create a wrapping script that parses the command line options, remove the unwanted options and executes the command given the new set of options:

#!/bin/sh

savedopts=-

printf 'Args in  = %s\n' "$*"

while getopts :bc opt; do
        case $opt in
                b|c) ;; # nothing
                *)
                        savedopts="$savedopts$OPTARG"
        esac
done

shift "$(( OPTIND - 1 ))"

set -- "$savedopts" -- "$@"

printf 'Args out = %s\n' "$*"

# Run the command:

some-command "$@"

This parses the command line, ignores the options b and c, and puts the rest of the options into $savedopts.

$savedopts is then used to run the wrapped command, together with any operands given on the original command line (separated with --).

We don't get any errors from getopts even though we ask it to parse options that it may not expect. This is due to the initial : in the first argument to getopts.

Test run:

$ ./script -abcd -b -c -- -bx -a foo bar
Args in  = -abcd -b -c -- -bx -a foo bar
Args out = -ad -- -bx -a foo bar
./script: some-command: not found

Thank you, this works very well! However, this seems overly complex for a simple problem. Except for when there are no options, the input always has exactly one -, followed by the letters. Is there no simple sed one-liner that behaves exactly like the code I put in my question? — rewire
– rewire, Commented Oct 18, 2022 at 10:52

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