Back Quote
      in many UnixShells, a BackQuoted BangBang is a very handy operation.
Back quotes put the result of a command on the command line Here's an example:
        grep -l wiki *          
      
      The above lists the names of all files containing the word wiki in the current directory.
        vi `!!`
      
      invokes the editor to modify the contents of the files the previous command just produced.