SH: how to convert the date "Nov 26 23:59:00 2022 GMT" to timestamp? - shell

Question

I want to convert the string "Nov 26 23:59:00 2022 GMT" to a timestamp 1669507140000. I checked the man date to get this command:
date -d "Nov 26 23:59:00 2022 GMT" +"%s"
But his returns: 1669507140 (the last 3 zeros are missing).
Can anyone tell me what I am missing? Thank you.

Answer 1

The version of the date command that I have on my system (YMMV) will show us what it is doing if we add the --debug flag to our invocation...
$ date -d "Nov 26 23:59:00 2022 GMT" +"%s" --debug
date: parsed date part: (Y-M-D) 2020-11-26
date: parsed time part: 23:59:00
date: parsed number part: year: 2022
date: parsed zone part: UTC+00
date: input timezone: parsed date/time string (+00)
date: using specified time as starting value: '23:59:00'
date: starting date/time: '(Y-M-D) 2022-11-26 23:59:00 TZ=+00'
date: '(Y-M-D) 2022-11-26 23:59:00 TZ=+00' = 1669507140 epoch-seconds
date: timezone: system default
date: final: 1669507140.000000000 (epoch-seconds)
date: final: (Y-M-D) 2022-11-26 23:59:00 (UTC)
date: final: (Y-M-D) 2022-11-27 07:59:00 (UTC+08)
1669507140
The debug log shows us the %s format will result in displaying seconds since epoch. Alternatively, nanosecond precision can be achieved using a modified format string (I added a .001 in the date string to prove it works):
$ date -d "Nov 26 23:59:00.001 2022 GMT" +"%s.%N" --debug
date: parsed date part: (Y-M-D) 2020-11-26
date: parsed time part: 23:59:00
date: parsed number part: year: 2022
date: parsed zone part: UTC+00
date: input timezone: parsed date/time string (+00)
date: using specified time as starting value: '23:59:00'
date: starting date/time: '(Y-M-D) 2022-11-26 23:59:00 TZ=+00'
date: '(Y-M-D) 2022-11-26 23:59:00 TZ=+00' = 1669507140 epoch-seconds
date: timezone: system default
date: final: 1669507140.001000000 (epoch-seconds)
date: final: (Y-M-D) 2022-11-26 23:59:00 (UTC)
date: final: (Y-M-D) 2022-11-27 07:59:00 (UTC+08)
1669507140.001000000
We can use a pipe to awk to round up to milliseconds for our final form (note I used .0005 in the date string here to show rounding):
$ date -d "Nov 26 23:59:00.0005 2022 GMT" +"%s.%N" | awk '{ printf("%d\n", int($0 * 1000) + (int($0 * 2000) % 2)) }'
1669507140001
One further note.... The following is the version of the date command I am using:
$ date --version
date (GNU coreutils) 8.30
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by David MacKenzie.