[Bug-tar] Have gnutar pass --no-name to gzip

[Michael D. Adams]

Is there some way to convince gnutar that it should pass "--no-name"
(or the C API equivalent) to gzip?  (This prevents gzip from embedding
the current time in the file [1].)

The reason I ask is that I need to pass "--no-name" to gzip (so
re-tar-ing the same file twice produces identical binary output).  I
could write it as a pipeline (e.g. "tar -cf - ... | gzip --no-name
>file.tar.gz"), but there are two problems with that.  First, gnutar
may[2] be more efficient at running gzip internally (e.g. if it uses a
library rather than spawning a gzip process).  Since this is in an
inner loop [3], I want to run things in the most efficient way
possible.  Second, I need to be able to detect any error codes coming
from tar but POSIX shells only report errors in the last command of
the pipeline.

Michael D. Adams

[1] I've also considered using other compression flags (e.g. -j for
bzip2 or -Z for compress) since they don't embed the current time in
their files, but they have other draw backs.  "bzip2" is just too
sloooow.  "compress" exits with error code 2 if the compressed file
would be larger than the original.  This is not a good thing to happen
in the middle of this particular script as catching that error
condition and recovering from it makes things difficult.

[2] Timing tests that I've run are inconclusive.

[3] Yes, I'm invoking tar hundreds of thousands of times which isn't
exactly efficient, but I need separate tar files in the output and so
I don't see any way around that part of the inefficiency.  Some
inefficiencies can't be avoided, but I'd like to avoid them where ever
possible.