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Notes below...
On 23/07/2025 08:56, Geoff Kuenning via GNU coreutils Bug Reports wrote:
Tested on coreutils 9.5 (gentoo) and 8.32 (OpenSuSE).
There seems to be an interesting interaction in the code that
parses relative dates in the --date switch; relative
specifications used with ISO 8601 base dates can give incorrect
results.
All tests below were run with a time zone of America/Los_Angeles.
The following date commands work fine:
$ date -d '2025-01-20T12:00:00Z +180 days'
Sat Jul 19 05:00:00 AM PDT 2025
$ date -d '2025-01-20T12:00:00-0800 +180 days'
Sat Jul 19 01:00:00 PM PDT 2025
However, omitting the time zone gives a surprising result that's
only one day later, and at a different time:
$ date -d '2025-01-20T12:00:00 +180 days'
Tue Jan 21 01:40:00 AM PST 2025
Adding --debug shows what's happening here:
$ date --debug -d '2025-01-20T12:00:00 +180 days'
date: parsed datetime part: (Y-M-D) 2025-01-20 12:00:00 UTC+02:20
date: parsed relative part: +1 day(s)
I.e. the "+180" is taken as a POSIX timezone offset in minutes,
and the "days" is taken as a relative +1 day.
There are lots of combinations and edge cases in date inputs unfortunately.
cheers,
Padraig
