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.
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CategoryCommandLine