Possible Duplicate:What does “--” (double-dash) mean?Single dashes - for single-character options, but double dashes -- for words? I was reading the man zip page and I found this examples:[...] using the commandunzip -p backup | tar xf -When [...]  For example,tar cf - . | zip | dd of=/dev/nrst0 obs=16kis equivalent totar cf - . | zip - - | dd of=/dev/nrst0 obs=16kI' like know the minus utility of these cases. Why two minus signs are written in the third case?
What good are the signs '-' (minus) in any Linux/UNIX commands?
linux;command line