GitHub Actions can't read `while (( "$#" ));` in .bash script [duplicate] - bash

Question

This question already has answers here:
Difference between sh and Bash
(11 answers)
Closed 2 months ago.
Given a GitHub Action file:
name: Pull Request
on:
pull_request:
branches: [main]
types: [opened, reopened, ready_for_review]
jobs:
build_and_test:
runs-on: ubuntu-latest
steps:
- name: Check out code
uses: actions/checkout#v3
- name: Run bash script
run: |
sh build.bash --a 3 --b 4
I'm unable to run the following build.bash file through GitHub Actions, instead getting the error build.bash: 17: 4: not found where line 17 corresponds with the line: while (( "$#" ));
#!/bin/sh
REPO_NAME="my-repo"
# Set defaults up top for clarity and define only once
A="1"
B="2"
usage()
{
echo "Usage: build.sh [--a version] [--b version]"
echo ""
echo "--a 'a' version to use. Defaults to $A."
echo "--b 'b' version to use. Defaults to $B"
exit 1
}
while (( "$#" ));
do
case "$1" in
-h|--help)
usage
;;
--a)
shift
A="$1"
shift
;;
--b)
shift
B="$1"
shift
;;
# Unknown option
*)
echo "Unrecognized option: $1"
usage
;;
esac
done
echo CLI args: --a=$A --b=$B
When ran locally, everything prints out as expected:
sh build.bash --a 3 --b 4
# CLI args: --a=3 --b=4
How do I ensure that running the same command in GitHub Actions returns the same value while maintaining a similar logic for parsing CLI arguments

Answer 1

The issue resolves if we run bash build.bash --a 3 --b 4 instead of sh build.bash --a 3 --b 4 in the GHA .yml file. Correspondingly, we should update the shebang with #! /bin/bash at the top of the .bash file.
Shoutout to #GordonDavisson and #DiegoTorresMilano for helping resolve this issue