Quickly getting to YYYY-mm-dd HH:MM:SS in Perl
When writing Perl scripts I frequently find the need to obtain the current time represented as a string formatted as YYYY-mm-dd HH:MM:SS
(say 2009-11-29 14:28:29
).
In doing this I find myself taking this quite cumbersome path:
man perlfunc
/localtime
to search for localtime - repeat开发者_如何学JAVA five times (/
+\n
) to reach the relevant section of the manpage- Copy the string
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
from the manpage to my script. - Try with
my $now = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $year, $mon, $mday, $hour, $min, $sec);
- Remember gotcha #1: Must add 1900 to $year to get current year.
- Try with
my $now = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $year+1900, $mon, $mday, $hour, $min, $sec);
- Remember gotcha #2: Must add 1 to $mon to get current month.
- Try with
my $now = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $year+1900, $mon+1, $mday, $hour, $min, $sec);
- Seems ok. Done!
While the process outlined above works it is far from optimal. I'm sure there is a smarter way, so my question is simply:
What is the easiest way to obtain a YYYY-mm-dd HH:MM:SS
of the current date/time in Perl?
Where "easy" encompasses both "easy-to-write" and "easy-to-remember".
Use strftime
in the standard POSIX
module. The arguments to strftime
in Perl’s binding were designed to align with the return values from localtime
and gmtime
. Compare
strftime(fmt, sec, min, hour, mday, mon, year, wday = -1, yday = -1, isdst = -1)
with
my ($sec,$min,$hour,$mday,$mon,$year,$wday, $yday, $isdst) = gmtime(time);
Example command-line use is
$ perl -MPOSIX -le 'print strftime "%F %T", localtime $^T'
or from a source file as in
use POSIX;
print strftime "%F %T", localtime time;
Some systems do not support the %F
and %T
shorthands, so you will have to be explicit with
print strftime "%Y-%m-%d %H:%M:%S", localtime time;
or
print strftime "%Y-%m-%d %H:%M:%S", gmtime time;
Note that time
returns the current time when called whereas $^T
is fixed to the time when your program started. With gmtime
, the return value is the current time in GMT. Retrieve time in your local timezone with localtime
.
Why not use the DateTime
module to do the dirty work for you? It's easy to write and remember!
use strict;
use warnings;
use DateTime;
my $dt = DateTime->now; # Stores current date and time as datetime object
my $date = $dt->ymd; # Retrieves date as a string in 'yyyy-mm-dd' format
my $time = $dt->hms; # Retrieves time as a string in 'hh:mm:ss' format
my $wanted = "$date $time"; # creates 'yyyy-mm-dd hh:mm:ss' string
print $wanted;
Once you know what's going on, you can get rid of the temps and save a few lines of code:
use strict;
use warnings;
use DateTime;
my $dt = DateTime->now;
print join ' ', $dt->ymd, $dt->hms;
Try this:
use POSIX qw/strftime/;
print strftime('%Y-%m-%d',localtime);
the strftime
method does the job effectively for me. Very simple and efficient.
Time::Piece (in core since Perl 5.10) also has a strftime function and by default overloads localtime and gmtime to return Time::Piece objects:
use Time::Piece;
print localtime->strftime('%Y-%m-%d');
or without the overridden localtime:
use Time::Piece ();
print Time::Piece::localtime->strftime('%F %T');
I made a little test (Perl v5.20.1 under FreeBSD in VM) calling the following blocks 1.000.000 times each:
A
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
my $now = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $year+1900, $mon+1, $mday, $hour, $min, $sec);
B
my $now = strftime('%Y%m%d%H%M%S',localtime);
C
my $now = Time::Piece::localtime->strftime('%Y%m%d%H%M%S');
with the following results:
A: 2 seconds
B: 11 seconds
C: 19 seconds
This is of course not a thorough test or benchmark, but at least it is reproducable for me, so even though it is more complicated, I'd prefer the first method if generating a datetimestamp is required very often.
Calling (eg. under FreeBSD 10.1)
my $now = `date "+%Y%m%d%H%M%S" | tr -d "\n"`;
might not be such a good idea because it is not OS-independent and takes quite some time.
Best regards, Holger
if you just want a human readable time string and not that exact format:
$t = localtime;
print "$t\n";
prints
Mon Apr 27 10:16:19 2015
or whatever is configured for your locale.
Time::Piece::datetime()
can eliminate T
.
use Time::Piece;
print localtime->datetime(T => q{ });
Short and sweet, no additional modules needed:
my $toDate = `date +%m/%d/%Y" "%l:%M:%S" "%p`;
Output for example would be: 04/25/2017 9:30:33 AM
In many cases, the needed 'current time' is rather $^T, which is the time at which the script started running, in whole seconds (assuming only 60 second minutes) since the UNIX epoch.
This to prevent that an early part of a script uses a different date (or daylight-saving status) than a later part of a script, for example in query-conditions and other derived values.
For that variant of 'current time', one can use a constant, also to document that it was frozen at compile time:
use constant YMD_HMS_AT_START => POSIX::strftime( "%F %T", localtime $^T );
Alternative higher resolution startup time:
0+ [ Time::HiRes::stat("/proc/$$") ]->[10]
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