Bttf is a command line datetime Swiss army knife
github.com102 points by burntsushi 15 hours ago
102 points by burntsushi 15 hours 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):
$ 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
$ 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
This is pretty neat. My proficiency with the command line is woefully underdeveloped and seeing examples like this help me see the possibilities.
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.
Perl's DateTime module was pretty solid, IIRC. One of the things I miss about using Perl.
Everyone talking about "biff" should be aware that it's actually "bttf" like "back to the future"
Don't jump to the conclusion that they all mis-read the name several hours ago, though.
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.
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.
I am a happy user of dateutils [0], but I will try out Biff and see which one is more ergonomic.
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.
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
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.
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.
Same dude that made jiff. Love that library, so I'm assuming biff is built on top of jiff.
also made ripgrep
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...".
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. :-)
And xsv. Burntsushi projects have certain quiet sensibility that I appreciate.
I only recently realized that xsv is now unmaintained. The author now suggests using qsv or xan.
% biff
2026 M05 28, Thu 17:27:46
Ahh, the month of M05
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
$ 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
$ BIFF_LOCALE=watwat biff time fmt -f '%c' '1 month'
2026 M06 28, Sun 06:39:50I came here to complain about this. Please read `LANG` like everything else :)
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
No, Biff informs the system whether you want to be notified when mail arrives during the current terminal session.
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.
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.
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
I dont think it's part of the unix standard. Biff sounds perfect
My decisions about naming aren't limited or prescribed by what is in a standard or not. :-)
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.
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
> 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?
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-...>
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` (!).
> 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
Those are:
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.
I've renamed the project to bttf :-)
That works on Debian ;-)
<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.
It was a great opportunity to name a unix tool "mcfly" or just "Marty" for time manipulation. Better luck next time, I guess.
docbrown would be more appropriate, as the character who's actually doing the time manipulation.
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.
https://crates.io/search?q=bttf
// backronym bttf stands for biff time to format
You win the naming contest. The project has been renamed: https://github.com/BurntSushi/bttf/pull/14
@dang - Could you update the post title please to say "bttf" instead of "Biff"? Thank you!
I don't think @ tags have any effect on HN, you'll want to email the mods directly: hn@ycombinator.com
I like this
also: back to the future
Intersting to notice that the name has been changed now when reading the post 12h late :-D
Naming is hard, sure, but doing some due diligence up front to see what's already being used isn't very difficult. Very neat tool.
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!
Back to the Future jokes never get old. I love it.
I still want one of those hover boards!
hellooo short-shorts
https://preview.redd.it/75ojrs5mzfcg1.jpeg?width=1024&auto=w...
Griff is still available for future projects or Buford if you create a throwback project.
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.
exactly. and chromium is a good looking space shooter with too few levels!
Yes I'm sure root is anxious to read all the mail in their local mailbox
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:
