What is the difference between
cp fileA fileB and
cp -- fileA fileB in Linux?
-- specifies the end of options. In your specific example this shouldn't make a difference but if you were using filename globbing such as:
cp * fileB to find a file and you had a file in your directory named
-R for example your command could potentially be:
cp -R dirA fileB
Which obviously wouldn't be the desired outcome. This is especially important when using commands like