bug#80974: Add Time conversion specifiers quick reference

On 09/05/2026 00:50, Bruno Haible via GNU coreutils Bug Reports wrote:
> Pádraig Brady wrote:
>> FORMAT  Example    Description
>>
>>    %%    %           a literal %
>>    %a    Sun         locale's abbreviated weekday name
>>    %A    Sunday      locale's full weekday name
>>    %b    Mar         locale's abbreviated month name
>>    %B    March       locale's full month name
>>    %c    '%a %x %X'  locale's date and time
>>    %C    20          century; like %Y, except omit last two digits
>>    %d    01          day of month
>>    %D    12/31/99    date (ambiguous); same as %m/%d/%y
>>    %e     1          day of month, space padded; same as %_d
>>    %F    1999-12-31  full date; like %+4Y-%m-%d
>>    %g    99          year of ISO week number (last two digits; 00-99); see %G
>>    %G    1999        year of ISO week number; normally useful only with %V
>>    %h    Mar         same as %b
>>    %H    23          hour (00..23)
>>    %I    01          hour (01..12)
>>    %j    365         day of year (001..366)
>>    %k     8          hour, space padded ( 0..23); same as %_H
>>    %l     9          hour, space padded ( 1..12); same as %_I
>>    %m    12          month (01..12)
>>    %M    59          minute (00..59)
>>    %n    \n          a newline
>>    %N    123456789   nanoseconds (000000000..999999999)
>>    %p    PM          locale's equivalent of AM or PM; blank if not known
>>    %P    pm          like %p, but lower case
>>    %q    4           quarter of year (1..4)
>>    %r    1:11:04 PM  locale's 12-hour clock time
>>    %R    23:59       24-hour hour and minute; same as %H:%M
>>    %s    1778169005  seconds since the Epoch (1970-01-01 00:00 UTC)
>>    %S    59          second (00..60)
>>    %t    \t          a tab
>>    %T    23:59:59    time; same as %H:%M:%S
>>    %u    7           day of week (1..7); 1 is Monday
>>    %U    52          week number of year; Sunday as first day of week (00..53)
>>    %V    52          ISO week number; Monday as first day of week (01..53)
>>    %W    52          week number of year; Monday as first day of week (00..53)
>>    %w    6           day of week (0..6); 0 is Sunday
>>    %x    12/31/99    locale's date (can be ambiguous)
>>    %X    23:59:59    locale's time representation
>>    %y    99          year (last two digits; 00..99)
>>    %Y    1999        year
>>    %z     +0400      +hhmm numeric time zone
>>    %:z    +04:00     +hh:mm numeric time zone
>>    %::z   +04:00:00  +hh:mm:ss numeric time zone
>>    %:::z  +04        numeric time zone to necessary precision; with :
>>    %Z     EDT        alphabetic time zone abbreviation
> 
> That's too many lines to search for. As a user, typically I ask:
>    1) I have a day to display; which directive can I use for it?
>    2) I have a time to display; which directive can I use for it?
> 
> Accordingly, I suggest to split this table into several smaller ones,
> namely one for each of:
>    - literal characters,
>    - date
>    - time
>    - date and time
>    - time zone
>    - nanosecond
> (similar to what I did in gnulib/lib/strftime.h).
Yes I suppose alphabetic is arbitrary.
I.e. users generally want to know "what letter corresponds to ...",
not "what corresponds to letter .".

cheers,
Padraig