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I wanted to get the month name on macOS 11.6, and I tried
datestrptimeBut I couldn't figure out what format specifier to use to display the month name.
After searching the internet, it seems that %b displays it.
I would like to know, where can I find all the information about specifiers within UNIX?
What's the official source, if man page doesn't have this info?
The manual for the C language function strftime() (man strftime) should contain all the date format specifiers across most Unix and Unix-like systems.
The strptime() function has to do with parsing strings into time values (which is not what you want to do), whereas strftime() has to do with outputting time values as formatted strings (which you want to do).
See also the POSIX specification for the strftime() interface.
MacOS is POSIX compliant, and is certified as such. Therefore you can also check the POSIX documentation for date. Here it does list the available format specifiers:
Conversion Specifications
%aLocale's abbreviated weekday name.
%ALocale's full weekday name.
%bLocale's abbreviated month name.
%BLocale's full month name....
It's a shame that the Mac's man page omits this useful information directly. However, it does contain this paragraph:
An operand with a leading plus (
+) sign signals a user-defined format string which specifies the format in which to display the date and time. The format string may contain any of the conversion specifications described in the strftime(3) manual page, as well as any arbitrary text. A newline (\n) character is always output after the characters specified by the format string.
In the SEE ALSO section there is also a reference to strftime(3).
Unfortunately, on my Mac at least, there is no strftime(3) man page, so it's not possible to get to further information without referencing documentation online. (Apparently the C library man pages are installed as part of XCode.)
strftime(3) man page is only present if you have XCode installed.
date can support.
For the date command, man dateis the right reading. It does list %b and %B, so you should have found it directly, without perusing the internet. Here's a somewhat recent copy of that man date.
But that is specific to that command. Other programs, libraries have different formats. You will need to look up their individual documentation.
man date doesn't show %b or %B. There is no info on any format specifier.
+) sign signals a user-defined format string .... The format string may contain any of the conversion specifications described in the strftime(3) manual page, ..." so man 3 strftime has the relevant list.
Jan 16, 2022 at 9:16
man date to the solution.
date specifically refers you to the man page for strftime.
dateprogram. It's FOSS, after all.datecommand accept at least one more format specifier thanstrftimedoes, namely%s, to print a rawtime_tvalue (seconds since 1970)..strftime, at least on macOS, is documented as accepting%s.