LINUX UNIX

What does “–” (double-dash) mean? (also known as “bare double dash”)

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:

Bash Code
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.

Bash Code
git checkout path/to/file.txt

Now suppose that the file is named master…

Bash Code
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.

Bash Code
git checkout -- master

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

Bash Code
git checkout -f      # wrong
git checkout -- -f   # right
READ  How To Packaging, Updating, and Installing Using Linux

About the author

Venkatesan Prabu

Venkatesan Prabu

Wikitechy Founder, Author, International Speaker, and Job Consultant. My role as the CEO of Wikitechy, I help businesses build their next generation digital platforms and help with their product innovation and growth strategy. I'm a frequent speaker at tech conferences and events.

Add Comment

Click here to post a comment