6 ms·

Bttf is a command line datetime Swiss army knife

183 points by burntsushi 5mo ago

yzydserd 5mo ago
No, Biff informs the system whether you want to be notified when mail arrives during the current terminal session.
- raverbashing 5mo ago
  Yes I'm sure root is anxious to read all the mail in their local mailbox
  - roryirvine 5mo ago
    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.
    - throw0101a 5mo ago
      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: * https://wiki.debian.org/Postfix#Forward_Emails https://wiki.debian.org/Postfix#Forward_Emails
- maybewhenthesun 5mo ago
  exactly. and chromium is a good looking space shooter with too few levels!
- throw0101a 5mo ago
  I.e., 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. * https://man.freebsd.org/cgi/man.cgi?query=biff https://man.freebsd.org/cgi/man.cgi?query=biff 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] * https://en.wikipedia.org/wiki/Biff_(Unix) https://en.wikipedia.org/wiki/Biff_(Unix)
  - teddyh 5mo ago
    Also: <https://manpages.debian.org/stable/biff/biff.1.en.html https://manpages.debian.org/stable/biff/biff.1.en.html>
  - dcminter 5mo ago
    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.
    - burntsushi 5mo ago
      Yeah this was before my time. I never did email from a terminal. Which probably explains why I was okay with naming it Biff. In any case, I've renamed the project to bttf: https://github.com/BurntSushi/bttf/pull/14 https://github.com/BurntSushi/bttf/pull/14
      - sourcegrift 5mo ago
        I dont think it's part of the unix standard. Biff sounds perfect
        burntsushi 5mo ago
        My decisions about naming aren't limited or prescribed by what is in a standard or not. :-)
      - 5mo ago
- burntsushi 5mo ago
  Yeah the name collision is unfortunate, but probably fine. The name Biff was just too good to pass up. 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 https://www.youtube.com/shorts/9Jabplo2pZU [1]: https://github.com/BurntSushi/jiff https://github.com/BurntSushi/jiff
  - throw0101c 5mo ago
    > Yeah the name collision is unfortunate, but probably fine. The name Biff was just too good to pass up. So if I do an "apt install biff" on Debian (or Ubuntu) what will happen? * https://packages.debian.org/search?keywords=biff 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?
    - burntsushi 5mo ago
      I honestly don't know. Which is... Not Great.
    - abrowne 5mo ago
      I know that if you want `fd` (https://github.com/sharkdp/fd https://github.com/sharkdp/fd) you need to `apt install fd-find` and which installs the binary `fdfind` (!).
    - dredmorbius 5mo ago
      Per Debian policy and precedence of the email notification utility, you'll install biff, the command-line email notification utility: <https://www.debian.org/doc/debian-policy/ch-binary.html#the-package-name https://www.debian.org/doc/debian-policy/ch-binary.html#the-...> <https://packages.debian.org/trixie/biff https://packages.debian.org/trixie/biff>
  - eb0la 5mo ago
    It was a great opportunity to name a unix tool "mcfly" or just "Marty" for time manipulation. Better luck next time, I guess.
- nine_k 5mo ago
  All short names, that is, pronounceable strings of 4 or maybe even 5 letters are already taken. Some of them taken many times over. I think fewer people now care about mail notifications in a terminal session than about wrangling datetimes on the command line.
  - deleted 5mo ago
    [deleted]
- dredmorbius 5mo ago
  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.
elcaro 5mo ago
% biff 2026 M05 28, Thu 17:27:46 Ahh, the month of M05
- croisillon 5mo ago
  just between a04 and j06 yes
  - raverbashing 5mo ago
    Looking forward to the J07 04 holiday
- burntsushi 5mo ago
  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
  - aftbit 5mo ago
    I came here to complain about this. Please read `LANG` like everything else :)
    - burntsushi 5mo ago
      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.
smartmic 5mo ago
I am a happy user of dateutils [0], but I will try out Biff and see which one is more ergonomic. [0]: https://www.fresse.org/dateutils/ https://www.fresse.org/dateutils/
- burntsushi 5mo ago
  Yes! dateutils is great! I have a comparison about it here: https://github.com/BurntSushi/biff/blob/master/COMPARISON.md#dateutils https://github.com/BurntSushi/biff/blob/master/COMPARISON.md... The comparison with GNU date is also likely informative.
jibaoproxy 5mo ago
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.
- cyberrock 5mo ago
  That's an interesting perspective because if I use America/New_York I would assume that it's subject to the laws of New York City. If I wanted a different DST regime I'd just use +4, +5, or a different city.
  - burntsushi 5mo ago
    That's a complaint against how time zones are themselves named and organized. See https://ftp.iana.org/tz/tzdb-2022b/theory.html https://ftp.iana.org/tz/tzdb-2022b/theory.html for all the gory details. Using +4 or +5 explicitly instead of a time zone when DST is relevant is bad juju. Then your arithmetic can become silently wrong in subtle ways when it cross a DST boundary.
    - cyberrock 5mo ago
      Ah I see, I didn't understand the original question properly. "Choose one side of DST or another" was meant for the time literal, not the TZ. That's my bad.
ramon156 5mo ago
Same dude that made jiff. Love that library, so I'm assuming biff is built on top of jiff.
- rippeltippel 5mo ago
  also made ripgrep
  - zokier 5mo ago
    And xsv. Burntsushi projects have certain quiet sensibility that I appreciate.
    - Crontab 5mo ago
      I only recently realized that xsv is now unmaintained. The author now suggests using qsv or xan.
  - darknavi 5mo ago
    So this is who I get to "blame" for LLMs constantly saying "I want to use `rg` but I see that it's not installed on this system...".
    - burntsushi 5mo ago
      ripgrep is a required dependency of codex when installing it via brew on macOS. So you should at least not see it if you fall into that scenario. :-)
    - dotancohen 5mo ago
      If you've got enough permissions on the device to install a local llm, go ahead and install rg. After a few decades of installing my pet toys on every *nix box I maintain, I've seriously scaled back. Yet I continue to install rg. I can think of only two other non-default Debian install tools that I use regularly, those are git and ncdu.
e40 5mo ago
I remember when biff was what we ran in a CSH to be informed of new email. I don’t remember if this was a local UCB tool or if it was part of BSD.
- deleted 5mo ago
  [deleted]
burntsushi 5mo ago
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 https://github.com/BurntSushi/ripgrep): $ git ls-files | bttf tag exec git log -n1 --format='%aI' | bttf time in system | bttf time sort | bttf time fmt -f '%a %Y-%m-%d %H:%M:%S' | bttf untag -f '{tag}|t{data}' ... Thu 2025-10-30 13:30:14 crates/ignore/Cargo.toml Sat 2025-11-29 14:11:38 crates/core/flags/lowargs.rs Wed 2025-12-17 11:38:12 tests/misc.rs Wed 2025-12-17 11:38:12 tests/util.rs 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 Mon 2026-05-25 23:56:53 CONTRIBUTING.md Tue 2026-05-26 08:32:43 AI_POLICY.md Or even ask for a specific time window: $ 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.
- Crontab 5mo ago
  Thank you for making cool stuff and sharing it with us.
- skydhash 5mo ago
  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).
onceonceonce 5mo ago
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.
- burntsushi 5mo ago
  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 More examples here: https://github.com/BurntSushi/biff/blob/master/GUIDE.md#datetime-sequences https://github.com/BurntSushi/biff/blob/master/GUIDE.md#date... Implementing the RFC 5545 recurrence rules was quite a lot of fun: https://github.com/BurntSushi/biff/blob/4c75d5cf6e09310e74ca74ad3abde48a73b648ab/src/ical.rs 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.
  - jayknight 5mo ago
    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.
sherr 5mo ago
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.
- space_ghost 5mo ago
  Perl's DateTime module was pretty solid, IIRC. One of the things I miss about using Perl.
  - sherr 5mo ago
    Yes, I agree. It was magic to me really. I still love Perl.
billbrown 5mo ago
Everyone talking about "biff" should be aware that it's actually "bttf" like "back to the future"
- JdeBP 5mo ago
  Don't jump to the conclusion that they all mis-read the name several hours ago, though. * https://news.ycombinator.com/item?id=48310191 https://news.ycombinator.com/item?id=48310191
- rellik 5mo ago
  Not to be confused with "biff" from "back to the future"
- jolmg 5mo ago
  There's a commit message that says otherwise: > The new name, bttf, is a backronym for "biff, time to format!" It credits this comment: https://news.ycombinator.com/item?id=48307552 https://news.ycombinator.com/item?id=48307552 However, "back to the future" might be more memorable. I'm surprised they didn't see it.
psim1 5mo ago
I think I would have instead changed the name to `marty`, who, in time, learned to think fourth-dimensionally.
- burntsushi 5mo ago
  Maybe. But it's longer and already taken on crates.io.
Ferret7446 5mo ago
I feel like this kind of tool has been completely obsoleted by LLMs (even local models). I've used similar tools such as tiny for Emacs, which is a DSL for generating text based on numeric ranges. Now, it's simply more efficient to ask AI.
- burntsushi 5mo ago
  Quite plausible. I built most of it in May 2025 (1 year ago) before I even looked at LLMs for coding, and announced it in Oct 2025[1]. I started it principally as a mechanism to dog-food Jiff[2]. Jiff has not been obsoleted by LLMs and is exactly the sort of thing an LLM would add as a dependency to a Rust project. This ended up being an extremely useful exercise because it did lead to some Jiff improvements. Fun fact: ripgrep started as something to dog-food the regex crate (with a focus on performance). I didn't originally build it to release to end users funnily enough. To be clear, I'm not implying bttf will follow the same path. I honestly probably agree with you at this point. I wouldn't have 1 year ago though. [1]: https://news.ycombinator.com/item?id=45608547 https://news.ycombinator.com/item?id=45608547 [2]: https://github.com/BurntSushi/jiff https://github.com/BurntSushi/jiff
- illiac786 5mo ago
  I believe AI-for-everything will become unsustainable financially for many and I’m genuinely curious to see how people deal with it. When to use it? When is it wasteful? My big hypothesis is that tokens are going to get much more expensive. Either that or OpenAI/anthropic are going bankrupt. I’m almost excited to find out, I have to admit. Your remark just reminded me of this, I went a bit off topic, I admit.
  - gandreani 5mo ago
    Have you tried DeepSeek V4 Flash? It's very competent and extremely cheap. I think Gemma 4 is also a good example of a capable small model. I mention these not only because they're cheap but because they can run on consumer devices. The "every year bigger and more capable SOTA model" trend is mirrored by "the every year smaller and more capable open source model" trend.
commandersaki 5mo ago
Looks great but I just can't see myself using a specialised tool and language for this. I think it's just easier to use ChatGPT or whatever for those one-offs, especially converting timestamps from a log.
esafak 5mo ago
cargo-binstall support would be nice. https://github.com/cargo-bins/cargo-binstall/blob/main/SUPPORT.md https://github.com/cargo-bins/cargo-binstall/blob/main/SUPPO...
kittikitti 5mo ago
This is a really great project. I plan on utilizing this in a function call for my preferred AI agent. Congratulations on this launch.
gullevek 5mo ago
$> brew install bttf Warning: No available formula with the name "bttf same with macports so it is pretty much not existing, cause I am not getting some binaries and drop them into some folder for some command line tool
- adammarples 5mo ago
  It's a cargo package. There's an installation readme...
liampulles 5mo ago
At my last company, I wrote a little tool for pretty printing our JSON logs. You pipe into it and it prints out. It's quite easy to write such a thing in Go, and useful for assigning preferred timezone conversions, and colors for your special common log items.
taffydavid 5mo ago
I misread the title as biff, and thought it was a back to the future reference. Turns out I need glasses AND it was a back to the future reference

183 points by burntsushi 5mo ago

yzydserd 5mo ago

No, Biff informs the system whether you want to be notified when mail arrives during the current terminal session.

raverbashing 5mo ago
Yes I'm sure root is anxious to read all the mail in their local mailbox
- roryirvine 5mo ago
  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.
  - throw0101a 5mo ago
    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: * https://wiki.debian.org/Postfix#Forward_Emails https://wiki.debian.org/Postfix#Forward_Emails
maybewhenthesun 5mo ago
exactly. and chromium is a good looking space shooter with too few levels!
throw0101a 5mo ago
I.e., 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. * https://man.freebsd.org/cgi/man.cgi?query=biff https://man.freebsd.org/cgi/man.cgi?query=biff 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] * https://en.wikipedia.org/wiki/Biff_(Unix) https://en.wikipedia.org/wiki/Biff_(Unix)
- teddyh 5mo ago
  Also: <https://manpages.debian.org/stable/biff/biff.1.en.html https://manpages.debian.org/stable/biff/biff.1.en.html>
- dcminter 5mo ago
  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.
  - burntsushi 5mo ago
    Yeah this was before my time. I never did email from a terminal. Which probably explains why I was okay with naming it Biff. In any case, I've renamed the project to bttf: https://github.com/BurntSushi/bttf/pull/14 https://github.com/BurntSushi/bttf/pull/14
    - sourcegrift 5mo ago
      I dont think it's part of the unix standard. Biff sounds perfect
      - burntsushi 5mo ago
        My decisions about naming aren't limited or prescribed by what is in a standard or not. :-)
    - 5mo ago
burntsushi 5mo ago
Yeah the name collision is unfortunate, but probably fine. The name Biff was just too good to pass up. 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 https://www.youtube.com/shorts/9Jabplo2pZU [1]: https://github.com/BurntSushi/jiff https://github.com/BurntSushi/jiff
- throw0101c 5mo ago
  > Yeah the name collision is unfortunate, but probably fine. The name Biff was just too good to pass up. So if I do an "apt install biff" on Debian (or Ubuntu) what will happen? * https://packages.debian.org/search?keywords=biff 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?
  - burntsushi 5mo ago
    I honestly don't know. Which is... Not Great.
  - abrowne 5mo ago
    I know that if you want `fd` (https://github.com/sharkdp/fd https://github.com/sharkdp/fd) you need to `apt install fd-find` and which installs the binary `fdfind` (!).
  - dredmorbius 5mo ago
    Per Debian policy and precedence of the email notification utility, you'll install biff, the command-line email notification utility: <https://www.debian.org/doc/debian-policy/ch-binary.html#the-package-name https://www.debian.org/doc/debian-policy/ch-binary.html#the-...> <https://packages.debian.org/trixie/biff https://packages.debian.org/trixie/biff>
- eb0la 5mo ago
  It was a great opportunity to name a unix tool "mcfly" or just "Marty" for time manipulation. Better luck next time, I guess.
nine_k 5mo ago
All short names, that is, pronounceable strings of 4 or maybe even 5 letters are already taken. Some of them taken many times over. I think fewer people now care about mail notifications in a terminal session than about wrangling datetimes on the command line.
- deleted 5mo ago
  [deleted]
dredmorbius 5mo ago
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.

elcaro 5mo ago

% biff 2026 M05 28, Thu 17:27:46 Ahh, the month of M05

croisillon 5mo ago
just between a04 and j06 yes
- raverbashing 5mo ago
  Looking forward to the J07 04 holiday
burntsushi 5mo ago
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
- aftbit 5mo ago
  I came here to complain about this. Please read `LANG` like everything else :)
  - burntsushi 5mo ago
    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.

smartmic 5mo ago

I am a happy user of dateutils [0], but I will try out Biff and see which one is more ergonomic. [0]: https://www.fresse.org/dateutils/ https://www.fresse.org/dateutils/

burntsushi 5mo ago
Yes! dateutils is great! I have a comparison about it here: https://github.com/BurntSushi/biff/blob/master/COMPARISON.md#dateutils https://github.com/BurntSushi/biff/blob/master/COMPARISON.md... The comparison with GNU date is also likely informative.

jibaoproxy 5mo ago

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.

cyberrock 5mo ago
That's an interesting perspective because if I use America/New_York I would assume that it's subject to the laws of New York City. If I wanted a different DST regime I'd just use +4, +5, or a different city.
- burntsushi 5mo ago
  That's a complaint against how time zones are themselves named and organized. See https://ftp.iana.org/tz/tzdb-2022b/theory.html https://ftp.iana.org/tz/tzdb-2022b/theory.html for all the gory details. Using +4 or +5 explicitly instead of a time zone when DST is relevant is bad juju. Then your arithmetic can become silently wrong in subtle ways when it cross a DST boundary.
  - cyberrock 5mo ago
    Ah I see, I didn't understand the original question properly. "Choose one side of DST or another" was meant for the time literal, not the TZ. That's my bad.

ramon156 5mo ago

Same dude that made jiff. Love that library, so I'm assuming biff is built on top of jiff.

rippeltippel 5mo ago
also made ripgrep
- zokier 5mo ago
  And xsv. Burntsushi projects have certain quiet sensibility that I appreciate.
  - Crontab 5mo ago
    I only recently realized that xsv is now unmaintained. The author now suggests using qsv or xan.
- darknavi 5mo ago
  So this is who I get to "blame" for LLMs constantly saying "I want to use `rg` but I see that it's not installed on this system...".
  - burntsushi 5mo ago
    ripgrep is a required dependency of codex when installing it via brew on macOS. So you should at least not see it if you fall into that scenario. :-)
  - dotancohen 5mo ago
    If you've got enough permissions on the device to install a local llm, go ahead and install rg. After a few decades of installing my pet toys on every *nix box I maintain, I've seriously scaled back. Yet I continue to install rg. I can think of only two other non-default Debian install tools that I use regularly, those are git and ncdu.

e40 5mo ago

I remember when biff was what we ran in a CSH to be informed of new email. I don’t remember if this was a local UCB tool or if it was part of BSD.

deleted 5mo ago
[deleted]

burntsushi 5mo ago

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 https://github.com/BurntSushi/ripgrep): $ git ls-files | bttf tag exec git log -n1 --format='%aI' | bttf time in system | bttf time sort | bttf time fmt -f '%a %Y-%m-%d %H:%M:%S' | bttf untag -f '{tag}|t{data}' ... Thu 2025-10-30 13:30:14 crates/ignore/Cargo.toml Sat 2025-11-29 14:11:38 crates/core/flags/lowargs.rs Wed 2025-12-17 11:38:12 tests/misc.rs Wed 2025-12-17 11:38:12 tests/util.rs 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 Mon 2026-05-25 23:56:53 CONTRIBUTING.md Tue 2026-05-26 08:32:43 AI_POLICY.md Or even ask for a specific time window: $ 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.

Crontab 5mo ago
Thank you for making cool stuff and sharing it with us.
skydhash 5mo ago
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).

onceonceonce 5mo ago

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.

burntsushi 5mo ago
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 More examples here: https://github.com/BurntSushi/biff/blob/master/GUIDE.md#datetime-sequences https://github.com/BurntSushi/biff/blob/master/GUIDE.md#date... Implementing the RFC 5545 recurrence rules was quite a lot of fun: https://github.com/BurntSushi/biff/blob/4c75d5cf6e09310e74ca74ad3abde48a73b648ab/src/ical.rs 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.
- jayknight 5mo ago
  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.

sherr 5mo ago

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.

space_ghost 5mo ago
Perl's DateTime module was pretty solid, IIRC. One of the things I miss about using Perl.
- sherr 5mo ago
  Yes, I agree. It was magic to me really. I still love Perl.

billbrown 5mo ago

Everyone talking about "biff" should be aware that it's actually "bttf" like "back to the future"

JdeBP 5mo ago
Don't jump to the conclusion that they all mis-read the name several hours ago, though. * https://news.ycombinator.com/item?id=48310191 https://news.ycombinator.com/item?id=48310191
rellik 5mo ago
Not to be confused with "biff" from "back to the future"
jolmg 5mo ago
There's a commit message that says otherwise: > The new name, bttf, is a backronym for "biff, time to format!" It credits this comment: https://news.ycombinator.com/item?id=48307552 https://news.ycombinator.com/item?id=48307552 However, "back to the future" might be more memorable. I'm surprised they didn't see it.

psim1 5mo ago

I think I would have instead changed the name to `marty`, who, in time, learned to think fourth-dimensionally.

burntsushi 5mo ago
Maybe. But it's longer and already taken on crates.io.

Ferret7446 5mo ago

I feel like this kind of tool has been completely obsoleted by LLMs (even local models). I've used similar tools such as tiny for Emacs, which is a DSL for generating text based on numeric ranges. Now, it's simply more efficient to ask AI.

burntsushi 5mo ago
Quite plausible. I built most of it in May 2025 (1 year ago) before I even looked at LLMs for coding, and announced it in Oct 2025[1]. I started it principally as a mechanism to dog-food Jiff[2]. Jiff has not been obsoleted by LLMs and is exactly the sort of thing an LLM would add as a dependency to a Rust project. This ended up being an extremely useful exercise because it did lead to some Jiff improvements. Fun fact: ripgrep started as something to dog-food the regex crate (with a focus on performance). I didn't originally build it to release to end users funnily enough. To be clear, I'm not implying bttf will follow the same path. I honestly probably agree with you at this point. I wouldn't have 1 year ago though. [1]: https://news.ycombinator.com/item?id=45608547 https://news.ycombinator.com/item?id=45608547 [2]: https://github.com/BurntSushi/jiff https://github.com/BurntSushi/jiff
illiac786 5mo ago
I believe AI-for-everything will become unsustainable financially for many and I’m genuinely curious to see how people deal with it. When to use it? When is it wasteful? My big hypothesis is that tokens are going to get much more expensive. Either that or OpenAI/anthropic are going bankrupt. I’m almost excited to find out, I have to admit. Your remark just reminded me of this, I went a bit off topic, I admit.
- gandreani 5mo ago
  Have you tried DeepSeek V4 Flash? It's very competent and extremely cheap. I think Gemma 4 is also a good example of a capable small model. I mention these not only because they're cheap but because they can run on consumer devices. The "every year bigger and more capable SOTA model" trend is mirrored by "the every year smaller and more capable open source model" trend.

commandersaki 5mo ago

Looks great but I just can't see myself using a specialised tool and language for this. I think it's just easier to use ChatGPT or whatever for those one-offs, especially converting timestamps from a log.

esafak 5mo ago

cargo-binstall support would be nice. https://github.com/cargo-bins/cargo-binstall/blob/main/SUPPORT.md https://github.com/cargo-bins/cargo-binstall/blob/main/SUPPO...

kittikitti 5mo ago

This is a really great project. I plan on utilizing this in a function call for my preferred AI agent. Congratulations on this launch.

gullevek 5mo ago

$> brew install bttf Warning: No available formula with the name "bttf same with macports so it is pretty much not existing, cause I am not getting some binaries and drop them into some folder for some command line tool

adammarples 5mo ago
It's a cargo package. There's an installation readme...

liampulles 5mo ago

At my last company, I wrote a little tool for pretty printing our JSON logs. You pipe into it and it prints out. It's quite easy to write such a thing in Go, and useful for assigning preferred timezone conversions, and colors for your special common log items.

taffydavid 5mo ago

I misread the title as biff, and thought it was a back to the future reference. Turns out I need glasses AND it was a back to the future reference