How to change the time zone string of date command?

Question

I'm curious about how to change the abbreviation of time zone shown by date command. Let the time zone unchanged, but how to change CST below to UTC+8?

clay@LAPTOP-3PP2093I:~$ date
Thu Dec  1 23:05:28 CST 2022

Thank you!

PS 1. OS is ubuntu 22.04

PP 2. My time zone is Asia/Taipei, therefore the result of date +%Z is CST. However I think this abbr is confusing, therefore hope it is shown as UTC+8.

PS 3. I tried a workaround, change time to Asia/Singapore. Yes, the result of date +%Z is +08. But I really don't want to change time zone.

Answer 1

With export TZ='<UTC+8>-8' you'd be defining the current timezone as being named UTC+8 and being 8 hours ahead of UTC all year round for past, current and future dates.

Then:

$ date +'%::z %Z'
+08:00:00 UTC+8

$ date
Thu  1 Dec 23:04:48 UTC+8 2022

To keep Asia/Taipei (with its historical changes in timezone), but change what %Z returns, you'd need to modify and recompile the tzdata from which it is derived.

apt source tzdata
sudo apt build-dep tzdata

Change the Taiwan section to:

# Rule  NAME    FROM    TO  -   IN  ON  AT  SAVE    LETTER/S
Rule    Taiwan  1946    only    -   May 15  0:00    1:00    9
Rule    Taiwan  1946    only    -   Oct 1   0:00    0   8
Rule    Taiwan  1947    only    -   Apr 15  0:00    1:00    9
Rule    Taiwan  1947    only    -   Nov 1   0:00    0   8
Rule    Taiwan  1948    1951    -   May 1   0:00    1:00    9
Rule    Taiwan  1948    1951    -   Oct 1   0:00    0   8
Rule    Taiwan  1952    only    -   Mar 1   0:00    1:00    9
Rule    Taiwan  1952    1954    -   Nov 1   0:00    0   8
Rule    Taiwan  1953    1959    -   Apr 1   0:00    1:00    9
Rule    Taiwan  1955    1961    -   Oct 1   0:00    0   8
Rule    Taiwan  1960    1961    -   Jun 1   0:00    1:00    9
Rule    Taiwan  1974    1975    -   Apr 1   0:00    1:00    9
Rule    Taiwan  1974    1975    -   Oct 1   0:00    0   8
Rule    Taiwan  1979    only    -   Jul 1   0:00    1:00    9
Rule    Taiwan  1979    only    -   Oct 1   0:00    0   8

# Zone  NAME        STDOFF  RULES   FORMAT  [UNTIL]
# Taipei or Taibei or T'ai-pei
Zone    Asia/Taipei 8:06:00 -   UTC+8:06    1896 Jan  1
            8:00    -   UTC+8   1937 Oct  1
            9:00    -   UTC+9   1945 Sep 21  1:00
            8:00    Taiwan  UTC+%s

Then build the new tzdata package with:

dpkg-buildpackage -b

Install the generated package.

Then:

$ export TZ=Asia/Taipei
$ date
Thu  1 Dec 23:17:41 UTC+8 2022
$ date -d 1979-08-01
Wed  1 Aug 00:00:00 UTC+9 1979
$ date -d 1892-06-01
Wed  1 Jun 00:00:00 UTC+8:6 1892

You'd need to redo that every time the Ubuntu source package is updated (which happens quite a few times a year, any time any government in any country decides of a new DST change date or rule for instance), so probably not practical.

If it's only date's output you have issues with, you can also do:

$ date +"$(locale date_fmt | sed 's/%Z/UTC%:z/')"
Fri  2 Dec 00:31:05 UTC+08:00 2022

in place of

$ date
Fri  2 Dec 00:31:05 CST 2022

Or:

$ date +"$(locale d_t_fmt | sed 's/%Z/UTC%:z/')"
Fri 02 Dec 2022 00:33:02 UTC+08:00

in place of:

$ date +%c
Fri 02 Dec 2022 00:33:02 CST

Those:

$ locale -k LC_TIME | grep fmt
d_t_fmt="%a %d %b %Y %T %Z"
d_fmt="%d/%m/%y"
t_fmt="%T"
t_fmt_ampm="%l:%M:%S %P %Z"
era_d_fmt=""
era_d_t_fmt=""
era_t_fmt=""
date_fmt="%a %e %b %H:%M:%S %Z %Y"

Can be changed by compiling a new locale with your preference:

localedef -i <(sed 's/%Z/UTC%z/g' /usr/share/i18n/locales/en_GB) \
          -f UTF-8 ~/.locales/en_GB.UTF-8@mytimezoneformat
export LOCPATH=~/.locales LC_TIME=en_GB.UTF-8@mytimezoneformat

(above installed in my home directory, but you could also do it system-wide and not to have to set $LOCPATH).

Then:

$ date
Fri  2 Dec 01:11:16 UTC+0800 2022
$ date +%c
Fri 02 Dec 2022 01:11:20 UTC+0800