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by JonathonW 2360 days ago
BSD tar on my Mac (running 10.15.2) has -a for tarfile creation (-c mode); it always autodetects the compression format in extraction mode (-z, -j, etc. are ignored if -x is specified). Not sure when either behavior would've been introduced; the somewhat-older machine I tested on (running 10.13) does not have -a but does have the autodetection behavior on extract.

-I, on the other hand (which, in gnutar, specifies a compression program to run the output through), appears to actually be GNU-specific. BSD tar makes -I synonymous with -T (specifying a file containing the list of filenames to be extracted or archived).

(Please don't use Zstandard if you care about cross-platform compatibility at all, though-- it's fine in controlled environments like an OS package manager, but I don't have it on my Mac, nor do I have it by default on my Ubuntu server (which is still sitting back on 16.04; I should fix that sooner or later).)
1 comments
Lammy 2360 days ago
As a FreeBSD user I was curious since I wouldn't want to learn to depend on an option only to find it doesn't exist in version n-1, and today I learned that FreeBSD's tar is contributed code from libarchive and not an in-tree thing like I assumed! https://github.com/freebsd/freebsd/blob/master/usr.bin/tar/M...

Looks like that option got merged in 2013: https://github.com/freebsd/freebsd/blame/24ac2fb6ec0610e60ac...

The textual libarchive changelog isn't super clear on it, and I didn't feel like digging further, but appears to have been introduced some time between libarchive 3.0.4 in 2012 and libarchive 3.1.2 in 2013: https://github.com/freebsd/freebsd/commit/366f42737cba40ceb2...

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JonathonW 2360 days ago
This got me digging a little further, and (as a consequence) I just learned something new and fun: the current libarchive-based BSD tar can create and extract a ton [1] of other formats, including ZIP, RAR, and 7Zip files!

That'll save me some time next time I need to extract one at the command line; I always end up having to look at unzip's man page to make sure it's actually going to do what I want, and the 7zip command line utility's kind of funky (and not installed by default most places). But 'tar -xvf filename' is permanently burned into my mind and pretty much always does exactly what I want.

[1] https://www.freebsd.org/cgi/man.cgi?query=libarchive-formats...

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