Recall that in any situation where a filename is stored in a variable, we must be careful when using it on a command line, because it might get interpreted as an option:
$ cp "$myvar" destdir
If myvar were a file named -alphabet-, this would result in a confusing error:
cp: invalid option -- 'h'
This is because the string was interpreted as a bundled set of options, and the letters a, l, and p are all valid options for the GNU cp command, but h is not.
We can address this one of two main ways; the first, for the commands that support it, is to use the -- terminator string option:
$ cp -- "$myvar" destdir
This signals to the cp command that every word after that argument is not an option, but (in this case) a file or directory name to operate on.
Unfortunately, while this is a very widespread convention, not...