Re: [Bug-tar] [patch v3] Bug / question in tar

[Paul Eggert]

Tim Kientzle wrote:
> If you really believe that sending output to /dev/null should not do anything, 
> make it a fatal error so people won't rely on it.

That would be silly, as it defeats the whole point of having a /dev/null 
for output.

At this point we're arguing only about theory, since GNU tar actually 
does read the files in this case.  But in other cases, programs avoid 
input as an optimization, and that's perfectly all right.  For example, 
'diff FOO FOO' doesn't read FOO twice, and there's nothing wrong with 
that.  (In fact, 'diff' doesn't read FOO even once.)  If GNU tar 
improved its performance in similar cases, there would be nothing wrong 
with that either.

It sounds like enough people are misusing GNU tar in the way you 
describe that, if we improved its performance in this case, we'd need to 
add a --be-stupid option so that tar would continue to read data that it 
doesn't need to.  (Perhaps you could come up with a better name for the 
option.  :-)