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Bttf is a command line datetime Swiss army knife

172 points by burntsushi

by burntsushi

7 subcomments

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

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.

by sherr

1 subcomments

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.

by e40

1 subcomments

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.

by gullevek

1 subcomments

$> 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

by psim1

1 subcomments

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

by taffydavid

0 subcomment

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

by liampulles

0 subcomment

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.

by smartmic

1 subcomments

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/

by billbrown

2 subcomments

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

by ramon156

1 subcomments

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

by kittikitti

0 subcomment

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

by elcaro

3 subcomments

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

by esafak

0 subcomment

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

by yzydserd

6 subcomments

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

by jibaoproxy

1 subcomments

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.

by onceonceonce

1 subcomments

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.

by commandersaki

0 subcomment

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.

by Ferret7446

3 subcomments

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.