How can I change the default date format (using LC_TIME)?

Question

How do I change the format of date command by modifying LC_TIME in locale?

Currently the day of month uses %e format. I need it to be displayed in %d format.

Below is the Current Format:

#date
Thu Aug 9 18:26:11 IST 2018

Expected format:

#date
Thu Aug 09 18:26:11 IST 2018

Here is my locale:

#locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE=en_IN
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

LC_TIME section in /usr/share/i18n/locales/en_US:

    LC_TIME
abday   "Sun";"Mon";"Tue";"Wed";"Thu";"Fri";"Sat"
day "Sunday";/
    "Monday";/
    "Tuesday";/
    "Wednesday";/
    "Thursday";/
    "Friday";/
    "Saturday"

week 7;19971130;1
abmon   "Jan";"Feb";/
    "Mar";"Apr";/
    "May";"Jun";/
    "Jul";"Aug";/
    "Sep";"Oct";/
    "Nov";"Dec"
mon "January";/
    "February";/
    "March";/
    "April";/
    "May";/
    "June";/
    "July";/
    "August";/
    "September";/
    "October";/
    "November";/
    "December"
% Appropriate date and time representation (%c)
d_t_fmt "%a %d %b %Y %r %Z"
%
% Appropriate date representation (%x)
d_fmt   "%m//%d//%Y"
%
% Appropriate time representation (%X)
t_fmt   "%r"
%
% Appropriate AM/PM time representation (%r)
t_fmt_ampm "%I:%M:%S %p"
%
% Strings for AM/PM
%
am_pm   "AM";"PM"
date_fmt "%F %Z"
END LC_TIME

Please let me know what I can do in order to get the expected format.

NOTE: I need to execute just date command without any formatting options.

Answer 1

In LC_TIME, there seems to be a separate way to specify the format for the date(1) command. This can be seen in 16.04's en_US locale definition:

% Appropriate date representation (date(1))   "%a %b %e %H:%M:%S %Z %Y"
date_fmt    "<U0025><U0061><U0020><U0025><U0062><U0020><U0025><U0065>/
<U0020><U0025><U0048><U003A><U0025><U004D><U003A><U0025><U0053><U0020>/
<U0025><U005A><U0020><U0025><U0059>"
END LC_TIME

These lines are missing from 17.04 and newer's en_US locale definition, but is still present in the C and POSIX locale files (so date maybe using these as a fallback).

If I do edit the en_US locale to add a date_fmt setting before END LC_TIME and update the locales, it works fine:

# grep date_fmt /usr/share/i18n/locales/en_US
date_fmt "%F %Z"
# env LC_TIME=en_US.UTF-8 date
2018-08-13 JST
# date
Mon Aug 13 15:25:14 JST 2018
# sed -i 's/date_fmt.*/date_fmt "%Y"/' /usr/share/i18n/locales/en_US
# locale-gen en_US.UTF-8
Generating locales (this might take a while)...
  en_US.UTF-8... done
Generation complete.
# env LC_TIME=en_US.UTF-8 date
2018

Answer 2

I think you'll find the answers you're looking for here:

https://unix.stackexchange.com/a/748687/279250

Short version, you can do it with command-line options, environment variables, or by adding a new locale. The post gives details on each of these. You may want slightly different format specifiers in yours, but you'll see where to put them and how to make them take effect.