Sends from epoch, for 1 year ago on MacOS / BSD?

Question

I'm trying to calculate the number of seconds since the Epoch, using date on MacOS BSD.

I can get a one year ago date string:

$ date -v -1y

Tue Apr 21 10:44:47 EST 2020

...but I can't figure out how to convert it into seconds since Epoch. Any suggestions?

Add `+%s`. See [`man strftime`](https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/strftime.3.html). — Gordon Davisson, Apr 21 '21 at 18:00
Awesome, if you make that an answer I will happily accept it! — qUEnbcAr, Apr 21 '21 at 18:21

score 0 · Accepted Answer · answered Apr 21 '21 at 19:11

Add +%s to tell it to print the datetime as seconds since the epoch:

date -v -1y +%s

The + is a date option to set the output format, and %s is strftime format for "seconds since epoch".

Portability note: while the +%s part is pretty standard and portable (though the %s format is not actually required by POSIX), the -v -1y part is wildly nonportable. With GNU date (e.g. on most Linuxes), you'd use something like --date='1 year ago' instead. On NetBSD, -d '1 year ago' works. Check your local man page to see what your system supports.

Sends from epoch, for 1 year ago on MacOS / BSD?

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