Change global positional parameters inside a Bash function

Question

Is there a way to set the positional parameters of a bash script from within a function?

In the global scope one can use set -- <arguments> to change the positional arguments, but it doesn't work inside a function because it changes the function's positional parameters.

A quick illustration:

# file name: script.sh
# called as: ./script.sh -opt1 -opt2 arg1 arg2

function change_args() {
    set -- "a" "c" # this doesn't change the global args
}

echo "original args: $@" # original args: -opt1 -opt2 arg1 arg2
change_args
echo "changed args: $@" # changed args: -opt1 -opt2 arg1 arg2
# desired outcome:        changed args: a c

Answer 1

As stated before, the answer is no, but if someone need this there's the option of setting an external array (_ARRAY), modifying it from within the function and then using set -- ${_ARRAY[@]} after the fact. For example:

#!/bin/bash

_ARGS=()

shift_globally () {
  shift
  _ARGS=$@
}

echo "before: " "$@"
shift_globally "$@"
set -- "${_ARGS[@]}"
echo "after: " "$@"

If you test it:

./test.sh a b c d
> before:  a b c d
> after:  b c d

It's not technically what you're asking for but it's a workaround that might help someone who needs a similar behaviour.