tar2rpm: add filename '-' as an alias for stdin and stdout

[totph]

When no filenames are given the informative message
"tar2pm: reading tar content from stdin, writing rpm data to stdout."
is printed to stderr. This can be suppressed by explicitly
specifying '-' for TARFILE and RPMFILE (if only TAR- or RPMFILE is
given the message reflects that).

Also updated usage() to reflect that, and rename FILE to
TARFILE/RPMFILE.

[jarondl]

Thanks for the contribution!

I'm not sure I understand the rationale (or indeed the solution). What do you care if some message is printed to stderr? In common practice apps ignore stderr. Can you explain the reasoning?

If this is about some kind of "quietness" or "verbosity", perhaps adding a flag for that would be better than magical behavior difference when you specify "-" or not.

(I'm not saying no to this PR, I just want to understand it better).

[jarondl]

/gcbrun

[totph]

This tries to follow the "silence is golden" rule of most (non-Windows) commandline tools, and - is the common way to specify stdin on the commandline, e.g. cat file1 - file3. Also, tar cv /path | tar2rpm .. prints the list of files, but also the one line from tar2rpm. Otherwise I would only expect stderr output on error, unless explicitly requested.

When no - is specified then printing a notice is helpful, as in "hey, not doing anything because I'm implicitly reading data from stdin (which might be the terminal)". Unlike, say, grep foo which will just sit there.

So, in my opinion no -quiet flag is needed, but I would add a notice to usage(). Or let me know if you would prefer a -quiet or -verbose flag.

[jarondl]

When no - is specified then printing a notice is helpful, as in "hey, not doing anything because I'm implicitly reading data from stdin (which might be the terminal)". Unlike, say, grep foo which will just sit there.

So, in my opinion no -quiet flag is needed, but I would add a notice to usage(). Or let me know if you would prefer a -quiet or -verbose flag.

Sounds good. Please add a notice to usage() saying that passing - explicitly will silence the message.

[totph]

Updated usage, and while writing the text I split the overloaded FILE into TARFILE and RPMFILE, and added the - logic to the output logic as well so it is symmetric. Pardon the slight feature creep :)