It is the same as calling anything (a shell script, a C program, a python program, …) from a shell
If calling from any Unix shell, and the parameter has spaces, then you need to quote it.
sh my-shell-script hi "hello guys" bye
You can also use single quotes, these are more powerful. They stop the shell from interpreting anything (
", etc, except
sh my-shell-script hi 'hello guys' bye
You should also quote every variable use within the function.
Note that in your example the arguments are falling apart before they get to the function (as they are passed to the script).
There is no way to do it automatically, in the script, as there is no way for the script to know which spaces are which (which words are together).