Double dash:

• The double dash “–” means end of command line flags i.e. it tells the preceding command not to try to parse what comes after command line options.
• It is actually part of the POSIX standard that — can be used to separate options from other arguments, so you will see it on commands like cp and mv (which are not part of Bash).
• — works to separate options from regular expressions in grep, but the canonical way is to use -e/–regexp

Example use:

you want to grep a file for the string -v – normally -v would be considered as the option to reverse the matching meaning (only show lines that do not match), but with — you can grep for string -v like this:

grep -- -v file 

A double dash ( — ) is used in bash built-in commands and there are more other commands to signify the end of command options, after which only positional parameters are accepted

Example:

Suppose you have a file named path/to/file.txt in my Git repository, and you want to revert changes on it.

git checkout path/to/file.txt

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Now suppose that the file is named master…

git checkout master

Whoops! That changed branches instead. The — helps to separate the tree you want to check out from the files you want to check out.

git checkout -- master

It also helps us if some freako added a file named -f to our repository:

git checkout -f      # wrong
git checkout -- -f   # right