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biff — A simple utility for doing datetime arithmetic, parsing, and formatting. More information: <https://

Submitted by: @import:tldr-pages·Mar 2, 2026·

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simpledatetimecommandbiffdoingcliforutility

Problem

How to use the biff command: A simple utility for doing datetime arithmetic, parsing, and formatting. More information: <https://github.com/burntsushi/biff>.

Solution

biff — A simple utility for doing datetime arithmetic, parsing, and formatting. More information: <https://github.com/burntsushi/biff>.

Print the current time in a format of your choosing:

biff time fmt {{[-f|--format]}} rfc3339 now

Print multiple relative times in one command:

biff time fmt {{[-f|--format]}} '%c' now -1d 'next sat' 'last monday' '9pm last mon'

Print the current time in another time zone and round it the nearest 15 minute increment:

biff time in Asia/Bangkok now | biff time round {{[-i|--increment]}} 15 {{[-s|--smallest]}} minute

Convert a time between two different time zone:

TZ='Japan' biff time in America/New_York 02:30

Print a past or future time relative to current time:

biff time add {{-1d|1d|1w|-1m|1y|...}} now

Add a complex duration to the current time:

biff time add '1 week, 12 hours ago' now

Find the duration since a date in the past and round it to the desired precision:

biff span since 2025-01-20T12:00 {{[-l|--largest]}} year

Find timestamps in a log file and reformat them into your local time in place:

biff tag lines /tmp/access.log | biff time in system | biff time fmt {{[-f|--format]}} '%c' | head {{[-n|--lines]}} 3 | biff untag {{[-s|--substitute]}}

Code Snippets

Print the current time in a format of your choosing

biff time fmt {{[-f|--format]}} rfc3339 now

Print multiple relative times in one command

biff time fmt {{[-f|--format]}} '%c' now -1d 'next sat' 'last monday' '9pm last mon'

Print the current time in another time zone and round it the nearest 15 minute increment

biff time in Asia/Bangkok now | biff time round {{[-i|--increment]}} 15 {{[-s|--smallest]}} minute

Convert a time between two different time zone

TZ='Japan' biff time in America/New_York 02:30

Print a past or future time relative to current time

biff time add {{-1d|1d|1w|-1m|1y|...}} now

Context

tldr-pages: common/biff

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