Tar syntax
 

I'm sure this is easy for the pros who hang out here, but I'm lost

info tar para 4.6 gives an example - two parts confuse me

the example
I'm confused by the 3rd and 4th args
in the 3rd, "--file=-" apparently <dash> is used as a wild card. I don't see this convention explained in the tar documentation and don't recognize it based on my limited undrstanding of the POSIX regular expression syntax

the 4th arg consists of a period - I dont understand why it is there

Maybe someone can help lift my ignorance
thanks
Dick

In general, the '-' notation is used as shorthand for either standard input or standard output, as appropriate to the scenario. In your example case I would say it means that the resulting tarball would be written to standard output. The '.' notation is the top directory from which to build the tarball. Do 'ls -la' at a shell prompt, and you will see the directory '.', referring to the toplevel directory specified, often the current working directory (as in this case).
--- rod.

info tar is the interminable info page. have fun. no manpage.

I use tar this way
tar -options where options include one from each line

c or x for create or extract
z or j for gzip or bzip2
v for verbose
f for filename which is the tar filename and has to be after the f

then if you are creating a tar,
- for stdin
/some/files/

e.g. tar -xzvf some.tar.gz to open it
tar -cjf some.tar.bz2 /mydir/* to tar the directory tree under mydir.