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strftime

strftime is similar to printf, but the format specifiers it processes are designed for representing the date and time components of a Unix time.
In C, such a Unix time is found in the tm struct.

Interesting format specifiers

Some, imho, interesting strftime format specifiers are;
Format specifier Possible result Comment
%T 12:16:18 ISO 8601 shorthand for HH:MM:SS, equivalent to %H:%M:%S
%F 2019-09-22 Equivalent to %Y-%m-%d
%y 19 Year with 2 digits
%Y 2019 Year with 4 digits
%m 03 Two digit month
%d 07 Two digit day of month
%H / %I 17 / 05 Two digit Hour. %H is 24 hours, %I 12 hours. (Use %p for AM and PM)
%M 18 Two digit Minute
%R 17:18 Same as %H:%M
%S 09 Two digit second. Note: 60 is possible because of leap seconds.
%s 1607924497 Unix time, not available on Windows
%c Sun Sep 22 12:16:18 2019
%z +01:00 Time zone
%C 20 Century number (trunc(year/100))

glibc extensions

glibc extends %m, %d, %s, %H, %M (and others?) so that a minus sign can be placed after the % in order to omit a leading zero: (%-m %-d %-S).

See also

formatting output of date.
vim script: strftime
strftime (and strptime)
Perl module POSIX
The SQLite function strftime.
Formatting dates in SQL Server

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