2 version improvements

[bmwiedemann]

in addition to #97
this includes guessing the version from release tarballs

tested to work on openSUSE
with https://github.com/mcrapet/plowshare/archive/v%{version}.tar.gz

[mcrapet]

Hi,

Here is my new version:
https://gist.github.com/mcrapet/fe8e8a32a3457bf3c597a00322120884

Could you review it?

[bmwiedemann]

Works for me (tested on openSUSE and Debian with dash), but you neglected the theoretical case of a non-GNU/Linux system with a 'date' that does not support -r.
and the original version would have supported strange mixes like BSD date on Linux or GNU date on a BSD... no idea how common those are. I think, MacOS X has the most BSD users these days.

[mcrapet]

• BSD date on Linux: I don't buy it because date is GNU coreutils.
• GNU date on BSD, possible like sed, but convention is to prefix a "gnu" or "g" letter (like gsed).

But as you said it is theoretically possible.
What about checking date --version (first line) instead of uname -s?

[bmwiedemann]

actually, I only care about GNU/Linux, so you may just ignore such esoteric cases.

[mcrapet]

Last call: see v2 gist. For me this is good. No more uname dependency.

[bmwiedemann]

+1 👍

[mcrapet]

Committed db87b3d.
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