Biff is a command line datetime Swiss army knife

bburntsushi about 13 hours ago 47 commentsRead Article on github.com

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burntsushi•about 5 hours ago

I'm the author of Biff. I just wanted to share a really cool example of something that Biff 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 |
        biff tag exec git log -n1 --format='%aI' |
        biff time in system |
        biff time sort |
        biff time fmt -f '%a %Y-%m-%d %H:%M:%S' |
        biff 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 |
        biff tag exec git log -n1 --format='%aI' |
        biff time in system |
        biff time cmp ge 2026-01-01 |
        biff time cmp lt 2026-04-01 |
        biff time sort |
        biff time fmt -f '%a %Y-%m-%d %H:%M:%S' |
        biff 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, `biff tag exec` is using parallelism under the hood to make this even faster.

Crontab•about 4 hours ago

Thank you for making cool stuff and sharing it with us.

skydhash•about 3 hours 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).

burntsushi•about 3 hours ago

Oh nice thank you!

sherr•36 minutes 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.

yzydserd•about 8 hours ago

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

throw0101a•about 5 hours 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

    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)

dcminter•about 2 hours 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•16 minutes 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

teddyh•about 5 hours ago

Also: <https://manpages.debian.org/stable/biff/biff.1.en.html>

burntsushi•about 5 hours 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

[1]: https://github.com/BurntSushi/jiff

jacobobryant•44 minutes ago

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!

[1] https://github.com/jacobobryant/biff

m463•about 1 hour ago

> 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)

throw0101c•about 5 hours 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

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?

abrowne•about 1 hour ago

I know that if you want `fd` (https://github.com/sharkdp/fd) you need to `apt install fd-find` and which installs the binary `fdfind` (!).

burntsushi•about 4 hours ago

I honestly don't know. Which is... Not Great.

eb0la•about 5 hours ago

It was a great opportunity to name a unix tool "mcfly" or just "Marty" for time manipulation. Better luck next time, I guess.

burntsushi•about 4 hours ago

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.

hk1337•about 3 hours ago

Griff is still available for future projects or Buford if you create a throwback project.

fnordpiglet•21 minutes ago

B1FF IS LIMITED TO 22 COLUMNZ

nine_k•about 4 hours 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.

maybewhenthesun•about 7 hours ago

exactly. and chromium is a good looking space shooter with too few levels!

raverbashing•about 8 hours ago

Yes I'm sure root is anxious to read all the mail in their local mailbox

roryirvine•about 6 hours 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•about 5 hours 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

e40•about 6 hours 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.

onceonceonce•about 1 hour 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•16 minutes 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#date...

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.

jibaoproxy•about 6 hours 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.

smartmic•about 8 hours 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/

burntsushi•about 5 hours ago

Yes! dateutils is great! I have a comparison about it here: https://github.com/BurntSushi/biff/blob/master/COMPARISON.md...

The comparison with GNU date is also likely informative.

ramon156•about 6 hours ago

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

rippeltippel•about 5 hours ago

also made ripgrep

zokier•about 2 hours ago

And xsv. Burntsushi projects have certain quiet sensibility that I appreciate.

Crontab•about 1 hour ago

I only recently realized that xsv is now unmaintained. The author now suggests using qsv or xan.

elcaro•about 8 hours ago

% biff

2026 M05 28, Thu 17:27:46

Ahh, the month of M05

burntsushi•about 5 hours 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•about 1 hour ago

I came here to complain about this. Please read `LANG` like everything else :)

croisillon•about 6 hours ago

just between a04 and j06 yes

raverbashing•about 6 hours ago

Looking forward to the J07 04 holiday