Converts a time as returned by the time function to an 9-element list with the time localized for the standard Greenwich time zone. Typically used as follows:
All list elements are numeric, and come straight out of the C `struct
tm'.  $sec, $min, and $hour are the seconds, minutes, and hours of the
specified time.  $mday is the day of the month, and $mon is the month
itself, in the range 0..11
 with 0 indicating January and 11
indicating December.  $year is the number of years since 1900.  That
is, $year is 123
 in year 2023.  $wday is the day of the week, with
0 indicating Sunday and 3 indicating Wednesday.  $yday is the day of
the year, in the range 0..364
 (or 0..365
 in leap years).  $isdst
is always 0
.
Note that the $year element is not simply the last two digits of the year. If you assume it is then you create non-Y2K-compliant programs--and you wouldn't want to do that, would you?
The proper way to get a complete 4-digit year is simply:
- $year += 1900;
 
And to get the last two digits of the year (e.g., '01' in 2001) do:
- $year = sprintf("%02d", $year % 100);
 
If EXPR is omitted, gmtime() uses the current time (gmtime(time)).
In scalar context, gmtime() returns the ctime(3) value:
- $now_string = gmtime; # e.g., "Thu Oct 13 04:54:34 1994"
 
If you need local time instead of GMT use the localtime builtin. 
See also the timegm
 function provided by the Time::Local
 module,
and the strftime(3) and mktime(3) functions available via the POSIX module.
This scalar value is not locale dependent (see perllocale), but is instead a Perl builtin. To get somewhat similar but locale dependent date strings, see the example in localtime.
See gmtime in perlport for portability concerns.