What are those double-dash (--) options in man?
 

When I look at man pages, most commands seem to have some options listed with a double dash "--" in front of them.

For instance, man rpm lists options:

--quiet Print as little as possible
-v Verbose

Why does the Verbose option use one dash but the Quiet option use two?


Thanks in advance,

Utah

As far as I can tell, switches that use a letter (like -a) only need a dash, but those that use a word, don't. But I have no idea why - probably something from Unix.

They are gnu additions to the options to make some of them clearer. The man pages in Slackware make a distinction between industry standard POSIX options and the gnu ones each being under their own section.

You live and learn :)

I think additionally that single character options can be strung together on a single '-'.

For example...

tar -xvzf source.tar.gz

instead of (but is functionally the same as)

tar -x -v -z -f source.tar.gz

'--' options are actually single options that are more than one letter.

So...

tar --xvzf source.tar.gz

would actually force the tar program to look for a single option named 'xvzf'.

You can also mix and match, such as

ls -al --co

which will list all (-a) of the contents of the current directory in long (-l) format and apply color (--co) to the display based on the type of file listed on the screen.

Hope that helped.