Invoke function in sh

invoke.sh

#!/usr/bin/env sh

a () {
	echo "invoke a"
}

b () {
	echo "invoke b"
}

if [ "$1" = "a" ]; then
	a
elif [ "$1" = "b" ]; then
	b
else
	echo -e "Invalid args\nUsage:invoke.sh [a|b]"
	exit 1
fi