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Time Usage With Perl

Brief summary of tips for using time functions in Perl:

But first a definition:

Some functions take a seconds argument and return the various date/time elements of seconds, hours, month, etc. I refer to this as the broken-down time list.

A broken-down time list example:
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst);

Functions returning a list of broken-down time elements will return them in the order listed above.

0 <= sec <= 60

0 <= min <= 59

0 <= hour <= 23

1 <= mday <= 31, the day of the month

0 <= mon <= 11 , 0=Jan, 1=Feb, 2=Mar, etc.

year has 1900 subtracted from it, i.e. years since 1900. The year 1999 is 99 and the year 2000 is 100.

0 <= wday <= 6 , the day of the week , 0=Sunday, 1=Monday, 2=Tuesday, etc.

1 <= yday <= 366 , the day of the year

isdst = {0,1} , 0=DST (Daylight Saving Time) not in effect, 1= DST in effect

The isdst argument will rarely be used and is not needed to accurately display the time, so we will ignore it in the rest of our discussion.

Now, the functions:

(times)[0] - returns CPU seconds and fractions of a second that the current process has been executing.

time() - returns the number of non-leap seconds since the epoch (January 1, 1970 UTC, on Unix systems)

gmtime(seconds) - returns list of broken-down time representing seconds in UTC
ex: ($sec,$min,$hour,etc...) = gmtime(time)
returns the current time in UTC. (isdst is always equal to 0 for UTC.)

timegm(broken-down time) - returns seconds
ex: $gmTimeInSeconds = timegm($sec,$min,$hour, etc...)

localtime(seconds) - returns list of broken-down times
ex: ($sec,$min,$hour,etc...) = localtime(time)
returns the current local time based on the current time zone setting (see #9, below)

timelocal(broken-down time) - returns seconds
ex: $localTimeInSeconds = timelocal($sec,$min,$hour,etc...)

The FutureQuest® server's time zone symbolic link is stored at /etc/localtime. This symbolic link currently points to /usr/share/zoneinfo/US/Eastern, the time zone in which the server is located.

The time zone environment variable is TZ. You set it like this:
$ENV{TZ} = ':/usr/share/zoneinfo/US/Eastern';

This sets the TZ environment variable to the US/Eastern time zone. Note the use of the leading ":" which is required. You can use 'ls' from telnet to get a listing of all the time zones contained in the /usr/share/zoneinfo directory and its subdirectories. Or, you can visit www.timezoneconverter.com/cgi-bin/tzref.tzc which lists all the timezones that can be used. Simply tack on whatever time zone you want to use to the string ':/usr/share/zoneinfo/'. Note that all time zone usage is case sensitive.

Example #1:

You have performed all your time/date operations using gmtime() and timegm() and now have your date/time represented as SECONDS stored in $TimeInSeconds and you want to display this time in the Europe/Paris time zone.

use Time::Local;
my @dayofweek = (qw(Sunday Monday Tuesday Wednesday Thursday Friday Saturday));
my @monthnames = (qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec));
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday);
$ENV{TZ} = ':/usr/share/zoneinfo/Europe/Paris';
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) = localtime($TimeInSeconds);
$year += 1900;
print "This date is $dayofweek[$wday], $monthnames[$mon] $mday, $year\n";
print "This time is $hour:$min:$sec\n";

Example #2:

You have performed all your time/date operations using gmtime() and timegm() and now have your date/time represented as a UTC broken-down time stored in the variables $sec, $min, etc., and you want to display this time in the Europe/Paris time zone.

use Time::Local;
my $TimeInSeconds;
#convert from UTC to Europe/Paris
$ENV{TZ} = ':/usr/share/zoneinfo/Europe/Paris';
#convert broken-down time to seconds in UTC
$TimeInSeconds = timegm($sec,$min,$hour,$mday,$mon,$year,$wday,$yday);
#convert the UTC seconds to broken-down time in time zone
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) = localtime($TimeInSeconds);

The above was submitted by Rich from TimeZoneConverter.com

For clean code, it is recommended to use File::stat module which is part of the standard distribution in version 5.004 and later.

Use method mtime() to get the last modification time. This is the time the file itself was modified last.

Instead you can also use stat.ctime which is the time directory information about the file was changed, not the file itself.

stat.atime is the last time the file was accessed.

 

 

 
 
use File::stat;
use Time::localtime;

$datetime_string = ctime(stat($file)->mtime);

print "file $file was updated at $datetime_string\n";


Newbee21369 has asked for the wisdom of the Perl Monks concerning the following question:
I'm trying to get the timestamp of a file in a directory. When I run the code shown below I get the following result.

Last change: Time::tm=ARRAY(0x200b6064)

How can I get the this format as my Result?
Last change: 2004111622


#!/usr/bin/perl

use Time::localtime;
$tm = localtime;

opendir(DIR,"/usr/path");
my @dir=grep { !/^\.+$/ } readdir(DIR);
closedir(DIR);
$file_count = 0;

foreach $file (@dir)
{
$mtime = (stat ($file))[9];
print "Last change:\t" . scalar localtime($mtime) . "\n";
}


2004-11-26 Janitored by Arunbear - added code tags, as per Monastery guidelines

Comment on Get file timestamp for a file in a directory
Select or Download Code
Re: Get file timestamp for a file in a directory
by steves (Curate) on Nov 26, 2004 at 19:03 UTC
Surround your code with <code> </code> tags so we can read it.
[reply]
Re: Get file timestamp for a file in a directory
by ikegami (Sage) on Nov 26, 2004 at 19:07 UTC
Change
print "Last change:\t" . scalar localtime($mtime) . "\n";
to
print "Last change:\t" . ctime(localtime($mtime)) . "\n";
as mention in the Time::localtime docs.
[reply]
[d/l]
[select]
Re^2: Get file timestamp for a file in a directory
by ikegami (Sage) on Nov 26, 2004 at 21:01 UTC
Now that your post is readable, I'd like to correct myself. POSIX::strftime will suit your formating needs, and you need to add the path to the file you're stating for it to work properly. Here's working code:

#!/usr/bin/perl

use strict;
use warnings;

use POSIX ();

my $dir = "/usr/path";

opendir(DIR, $dir);
my @dir = grep { !/^\.+$/ } readdir(DIR);
closedir(DIR);

foreach (@dir)
{
my $file = "$dir/$_";
my $mtime = (stat($file))[9];
print "Last change:\t"
. POSIX::strftime("%Y%m%d", localtime($mtime))
. "\n";
}

[reply]
[d/l]
[select]
Re: Get file timestamp for a file in a directory
by steves (Curate) on Nov 26, 2004 at 19:28 UTC
Yes, your use of Time::localtime is the key. It overrides the built-in localtime. If you use the built-in, it returns a ctime(3) like string. But in either case, a ctime string isn't going to give you that 2004111622 format in most cases. To get a specific date format, you'd also want to incorporate something like a call to the POSIX strftime function.

I can't tell for sure, but it looks like you may also be trying to stat the base file name only: since you open the directory, you'd need to prepend the directory. Otherwise it will only work if you run it from that directory.
[reply]
Re: Get file timestamp for a file in a directory
by Newbee21369 (Novice) on Nov 27, 2004 at 16:45 UTC
Thanks for all your help!

 



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