I'm the author of Bttf. I just wanted to share a really cool example of something that Bttf can do that I _think_ is kinda hard to do otherwise. (And also, I want to make an assertion about it and I hope this will lead to me being wrong and learning something new.)
The use case is: "I want to see a list of all files in a repository, sorted in ascending order of when it was most recently changed according to source control. I also want to highlight the time with color, make it be in local time and format it in my own bespoke way using strftime." Here's the full command (run from the root of https://github.com/BurntSushi/ripgrep):
$ git ls-files |
bttf tag exec git log -n1 --format='%aI' |
bttf time in system |
bttf time cmp ge 2026-01-01 |
bttf time cmp lt 2026-04-01 |
bttf time sort |
bttf time fmt -f '%a %Y-%m-%d %H:%M:%S' |
bttf untag -f '{tag}|t{data}'
Thu 2026-02-12 20:39:46 crates/ignore/src/default_types.rs
Fri 2026-02-20 16:06:29 crates/core/flags/config.rs
Fri 2026-02-27 11:25:19 GUIDE.md
Fri 2026-02-27 11:25:19 crates/core/flags/defs.rs
If you run this on a big repository, it will take quite a lot of time because `git log -n1` takes a long time. I think this is the fastest way to get the most recent commit time on a single file? (That's the assertion that I hope someone can correct me on!) In any case, `bttf tag exec` is using parallelism under the hood to make this even faster.
Quick Note: You can put the pipe operator where your backslash is and you won’t have to escape the newline character. Works in bash, zsh and ksh (what I’ve tested).
Respect for programming this. I did some date/time calculations a few years ago using Perl and it was full of corner cases and trouble. Did I enjoy it? I enjoyed seeing it work. Hopefully with the right answers! This tool looks great.
The thing Biff gets right that gnu `date` and most stdlib datetime APIs get wrong: it treats "civil time" and "absolute instants" as different types. You cannot answer "what's 30 days from 2024-03-08 in America/New_York" without picking a side — DST means that's either 29d23h or 30d0h of elapsed time, and most APIs silently pick one without telling you.
Jiff (the underlying Rust crate) gets this from Temporal in TC39, which is the first time JS standards have led anything datetime-shaped. Hopefully the rest of the ecosystem catches up — Python's `zoneinfo` only landed in 3.9 and `datetime.timezone` still has sharp edges.
been hand-rolling date -d plus a wrapper script for newsletter scheduling for years. Stuff like "next second Tuesday after a holiday" and "convert these timestamps to a reader's local time before send". biff time seq monthly -w 2-tue would have replaced about 40 lines of bash for me.
Yes!!! To spell it out (with the new biff -> bttf name):
$ bttf time seq monthly -w 2-tue -u 1y | bttf time fmt -f '%c'
Tue, Jun 9, 2026, 11:15:11 AM EDT
Tue, Jul 14, 2026, 11:15:11 AM EDT
Tue, Aug 11, 2026, 11:15:11 AM EDT
Tue, Sep 8, 2026, 11:15:11 AM EDT
Tue, Oct 13, 2026, 11:15:11 AM EDT
Tue, Nov 10, 2026, 11:15:11 AM EST
Tue, Dec 8, 2026, 11:15:11 AM EST
Tue, Jan 12, 2027, 11:15:11 AM EST
Tue, Feb 9, 2027, 11:15:11 AM EST
Tue, Mar 9, 2027, 11:15:11 AM EST
Tue, Apr 13, 2027, 11:15:11 AM EDT
Tue, May 11, 2027, 11:15:11 AM EDT
I'm quite proud of it, because if you look at the implementation, it's almost entirely about dealing with the specification rules. All of the datetime bullshit (including handling time zones) is all deferred to Jiff.
Plus, the tests are nearly 4,000 lines. While the implementation is 2,000 lines.
I implemented those recursion rules (probably very poorly) years ago. I still often think about the ways I did and probably should have handled those. It was an interesting problem.
This is a fair critique actually. And this shouldn't be the default. It is for now because I haven't gotten around to making Biff read your POSIX locale settings and converting them to a Unicode locale. If you build with `cargo build --release --features locale` (or get Biff from a release binary), then you can do:
$ BIFF_LOCALE=en-US biff
Thu, May 28, 2026, 6:38:09 AM EDT
If that doesn't work, then you can enable logging to see an error message:
$ BIFF_LOCALE=watwat BIFF_LOG=warn biff
2026-05-28T06:39:08.876336708-04:00[America/New_York]|WARN|src/main.rs:76: reading `BIFF_LOCALE` failed, using unknown locale `und`: failed to parse `BIFF_LOCALE` environment variable: The given language subtag is invalid
2026 M05 28, Thu 06:39:08
What you're seeing is what ICU4X does when the user's locale is unknown or undetermined. The `M` prefix occurs to indicate that the number is the month, and is unrelated to the name. For example:
$ BIFF_LOCALE=watwat biff time fmt -f '%c' '1 month'
2026 M06 28, Sun 06:39:50
Oh yes definitely. Was always the plan. I was honestly just hoping someone would publish a crate to do that for me.
To be clear, I don't mean publishing a crate to read an environment variable. Of course. I mean a crate that converts a POSIX locale into a Unicode locale.
I guess there's probably a 20% solution that gets 80% of the way there. e.g.,
$ BTTF_LOCALE="$(echo $LANG | sed 's/_/-/' | sed 's/\..*//')" bttf
Thu, May 28, 2026, 11:46:21 AM EDT
If Biff just did that as a stop-gap until the full solution lands, I bet it would work in lots of cases.
NAME
biff -- be notified if mail arrives and who it is from
[…]
HISTORY
The biff command appeared in 4.0BSD. It was named after the dog of
Heidi Stettner. He died in August 1993, at 15.
Eric Cooper, a student contemporary to Foderero and
Stettner, reports that the dog would bark at the mail
carrier,[4][5] making it a natural choice for the name
of a mail notification system. Stettner herself
contradicts this.[3][6]
From the excellent "A Quarter Century of UNIX" (by the late Peter H. Salus):
Heidi would bring her dog with her to class and to her office. He was a very friendly dog, and a lot of the students enjoyed throwing a ball for him down the corridor to fetch. He even had his picture on the bulletin board with the graduate students: the legend read that he was working on his Ph.Dog. John decided to name the program after the dog: Biff. According to Heidi, John and Bill Joy then spent a lot of time trying to compose an explanation for biff - they came up with "Be notified if mail arrived." Biff, who died in August 1993, at 15, once got a B in a compiler class. According to Heidi, the story of Biff barking at the mailman is a scurrilous canard.
One of my favourite bits of trivia from that excellent book, but hardly anyone I bump into these days knows anything about that kind of multi-user Unix experience/environment these days. I barely caught any of it myself.
If I type in "biff" on a Debian CLI, what should I expect the behaviour of the program that is executed to be? Will it be something about mail or time?
> Yeah the name collision is unfortunate, but probably fine.
collisions, lol
% apt-cache search biff
biff - a mail notification tool
gnubiff - mail notification program for GNOME (and others)
wmbiff - Dockable app that displays information about mailboxes
xlbiff - mail notification pop-up with configurable message scans
(along with 9 more matches without biff in command name)
2. All mail-notification utilities, as was the original biff.
And since we're mentioning Debian, it has a policy requiring unique names within the Debian archive to be unique. Precedence goes to the earlier software packaged. Installed programs must also have unique names within a given system. The datetime Swiss army knife utility discussed here violates both policies.
That's... not terrible. Biff isn't exactly popular (yet?), so a name change isn't out of the question. Both of those names (and `biff`) are already taken on crates.io. Which is maybe not a huge problem. IDK. Naming is hard.
I did. I always do. I just missed this one. Or if I saw it, it didn't register for me and felt like it was just an old archaic tool. Which... is probably still true, but I under-estimated its mindshare. Just an honest unknown unknown.
As the author of a different project also named Biff, I do have to warn you that half the comments on your HN posts will be people quoting back to the future--though I haven't decided yet if that's annoying or an engagement hack!
For those confused by this and a few similar threads/comments: the project name was originally "biff", but that was changed apparently due to the discussion on this submission, which has been retitled.
Sending mail to root@<whatever> really did use to be a pretty reliable way of getting somebody useful's attention - the early-to-mid 90s equivalent of making a "Can someone from Google please unlock my account?" post on HN.
Under Debian/Ubuntu, when Postfix is installed, part of the standard list of questions that dpkg-reconfigure asks you is how you want mail flow to work: you can give it a central smarthost. So any local mail gets sent on, and on the central mail hub you can tell it to send root@ to someplace useful:
The use case is: "I want to see a list of all files in a repository, sorted in ascending order of when it was most recently changed according to source control. I also want to highlight the time with color, make it be in local time and format it in my own bespoke way using strftime." Here's the full command (run from the root of https://github.com/BurntSushi/ripgrep):
Or even ask for a specific time window: If you run this on a big repository, it will take quite a lot of time because `git log -n1` takes a long time. I think this is the fastest way to get the most recent commit time on a single file? (That's the assertion that I hope someone can correct me on!) In any case, `bttf tag exec` is using parallelism under the hood to make this even faster.* https://news.ycombinator.com/item?id=48310191
Jiff (the underlying Rust crate) gets this from Temporal in TC39, which is the first time JS standards have led anything datetime-shaped. Hopefully the rest of the ecosystem catches up — Python's `zoneinfo` only landed in 3.9 and `datetime.timezone` still has sharp edges.
[0]: https://www.fresse.org/dateutils/
The comparison with GNU date is also likely informative.
Implementing the RFC 5545 recurrence rules was quite a lot of fun: https://github.com/BurntSushi/biff/blob/4c75d5cf6e09310e74ca...
I'm quite proud of it, because if you look at the implementation, it's almost entirely about dealing with the specification rules. All of the datetime bullshit (including handling time zones) is all deferred to Jiff.
Plus, the tests are nearly 4,000 lines. While the implementation is 2,000 lines.
2026 M05 28, Thu 17:27:46
Ahh, the month of M05
To be clear, I don't mean publishing a crate to read an environment variable. Of course. I mean a crate that converts a POSIX locale into a Unicode locale.
I guess there's probably a 20% solution that gets 80% of the way there. e.g.,
If Biff just did that as a stop-gap until the full solution lands, I bet it would work in lots of cases.Heidi would bring her dog with her to class and to her office. He was a very friendly dog, and a lot of the students enjoyed throwing a ball for him down the corridor to fetch. He even had his picture on the bulletin board with the graduate students: the legend read that he was working on his Ph.Dog. John decided to name the program after the dog: Biff. According to Heidi, John and Bill Joy then spent a lot of time trying to compose an explanation for biff - they came up with "Be notified if mail arrived." Biff, who died in August 1993, at 15, once got a B in a compiler class. According to Heidi, the story of Biff barking at the mailman is a scurrilous canard.
One of my favourite bits of trivia from that excellent book, but hardly anyone I bump into these days knows anything about that kind of multi-user Unix experience/environment these days. I barely caught any of it myself.
In any case, I've renamed the project to bttf: https://github.com/BurntSushi/bttf/pull/14
The name comes from the fact that Biff is a character in Back to the Future, and it rhymes with Jiff[1]. Jiff is the datetime library that Biff uses.
"Make like a tree and get out of here!" https://www.youtube.com/shorts/9Jabplo2pZU
[1]: https://github.com/BurntSushi/jiff
So if I do an "apt install biff" on Debian (or Ubuntu) what will happen?
* https://packages.debian.org/search?keywords=biff
If I type in "biff" on a Debian CLI, what should I expect the behaviour of the program that is executed to be? Will it be something about mail or time?
<https://www.debian.org/doc/debian-policy/ch-binary.html#the-...>
<https://packages.debian.org/trixie/biff>
collisions, lol
(along with 9 more matches without biff in command name)1. Not precise name collisions.
2. All mail-notification utilities, as was the original biff.
And since we're mentioning Debian, it has a policy requiring unique names within the Debian archive to be unique. Precedence goes to the earlier software packaged. Installed programs must also have unique names within a given system. The datetime Swiss army knife utility discussed here violates both policies.
As Debian policy is used both for Debian and derived distros (see: <https://en.wikipedia.org/wiki/List_of_Linux_distributions#De...> for a partial listing), it has considerable influence.
<https://packages.debian.org/search?keywords=bttf>
Might want to ping the mods (hn@ycombinator.com) to update this submission title.
Edit: I'd typoed "bttf" as "btff" initially. Corrected shows partial but not exact matches on "libttfautohint1" and variants.
// backronym bttf stands for biff time to format
[1] https://github.com/jacobobryant/biff
I still want one of those hover boards!
https://preview.redd.it/75ojrs5mzfcg1.jpeg?width=1024&auto=w...
I think fewer people now care about mail notifications in a terminal session than about wrangling datetimes on the command line.
* https://wiki.debian.org/Postfix#Forward_Emails