In our mkcd example, we preceded both calls to "$1" with a double dash, --, the option terminator string. This syntax specifies a point beyond which further arguments are meant as argument strings for the program, often filenames, and not as options, even if they start with hyphens, such as -dirname-.
This is so that the mkdir and cd commands know that whatever we pass in as $1 is not an option to the command, such as -p or --version, but a directory name on which to operate. Most commands that accept options use this syntax to separate options from filenames or other words, including bash itself:
bash$ bash --version GNU bash, version 4.4.23(1)-release (x86_64-pc-linux-gnu) bash$ bash -- --version ...
