You can test, if the script was called with an argument:

[[ -z "$@" ]] && printf "No input\n" || printf "Input: %q\n" "$@"

Which means: if the length of the arguments ( $@) is zero (-z) then print "No input" else print the string in escaped form. I don't not, what you want to achieve, but if you try to escape strings, check the %q option of printf.

If you call the testscript this way:

testscript "h's m"

it will give you:

Input: h\'s\ m