Cannot show UNIX epoch with `-when 0`

[jnd-au]

Currently tz -when 0 will show the current (real) time instead of the UNIX epoch 0. This is a counter-intuitive and unfortunate. It would be good if -when 0 works the same way as -when 1 and -when -1. It would also be nice if ISO 8601/RFC 3339 date-times could be parsed, as this means tz would become quite versatile for developers to see and convert between seconds and timestamps.

[oz]

• I think it's fine to fix how -when 0 behave to match the UNIX epoch. 👍🏻
• But I'd rather not start parsing random formats for now. 👎🏻

If we add support for RFC3339 dates, we're opening the door to many many more human friendly (and non-human friendly) representations too. Like + 1 week, +1d, years, days, or all of go's time durations, and the many incompatible date formats in existence.

Relying on established tools like date works fine.

• 3 months from now is: tz -when $( date -d '+3 month' +%s ) (or date -v+3m +%s on MacOS/BSD).
• To use an RFC3339 date: tz -when $( date -d "2024-10-28T15:10:06Z" +%s ), or date -j -f "%Y-%m-%dT%H:%M:%SZ" "2024-10-28T15:10:06Z" +%s on MacOS/BSD (yay).

[jnd-au]

Okay, but hopefully you will reconsider the latter. ISO 8601 / RFC 3339 are standard and common, not random, and it would be good for tz to support at least one standard, international, platform-independent format. UNIX seconds are a platform-specific notion, and as you noted above, date isn’t even standard between GNU/Linux and BSD. UNIX seconds are especially inconvenient and unintuitive for Windows users, who face multiple steps to use -when with PowerShell e.g. have to convert the time to UTC, then convert to UNIX seconds, then trim the fractional part because tz won’t parse it.