Christopher Juckins

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==== Perl Manipulating Date Strings ====

Print file modification times:
<code>
$filename = "201010211800_a.png";
$mtime = (stat $filename)[9];
chomp($mtime);
$mtime_date = `/bin/date --date='Jan 1, 1970 00:00:00 +0000 + $mtime seconds' '+%A, %d %B %Y %H:%M:%S %Z'`;

Output is: Thursday, 21 October 2010 22:21:49 UTC
</code>

Querying a specific timezone to determine DST:
<code>
[cjuckins@lnxopc2: ~]$ zdump America/New_York
America/New_York  Tue May  3 13:41:20 2011 EDT

[cjuckins@lnxopc2: ~]$ zdump America/Los_Angeles
America/Los_Angeles  Tue May  3 10:41:52 2011 PDT
</code>

Manipulating date/time from NWS text products:
<code>
If you take the date/time line from a current text product, such as:

806 PM EST TUE 3 JAN 2012

Add a colon to the hour/minute:

8:06 PM EST TUE 3 JAN 2012

You can feed that string directly into the linux date command and
manipulate it forward and backward by any amount of time and then print
it out in the same format.

Forward 6 hours:
$ date --date="8:06 PM EST TUE 3 JAN 2012 6 hours" "+%I%M %p %Z %a %d %b
%Y" | sed 's/^0//' | sed 's/\s0/ /g' | sed 's/./\u&/g'
206 AM EST WED 4 JAN 2012

Forward 30 minutes:
date --date="8:06 PM EST TUE 3 JAN 2012 30 minutes" "+%I%M %p %Z %a %d
%b %Y" | sed 's/^0//' | sed 's/\s0/ /g' | sed 's/./\u&/g'
836 PM EST TUE 3 JAN 2012

Backward 12 hours:
date --date="8:06 PM EST TUE 3 JAN 2012 -12 hours" "+%I%M %p %Z %a %d %b
%Y" | sed 's/^0//' | sed 's/\s0/ /g' | sed 's/./\u&/g'
806 AM EST TUE 3 JAN 2012

The 1st sed strips any leading zeros at the beginning of the line, the
2nd sed strips any other leading zeros, and the final sed makes it all
UPPER.
</code>

Other file stats info:
[[http://perldoc.perl.org/functions/stat.html]]

Using Linux 'date' to print a time:
<code>
[juckins@lightning: /var/www/html/amtrak_status]$ date --date="Sat Nov 19 2011 11:00 pm"
Sat Nov 19 23:00:00 EST 2011
</code>

More examples of 'date' to compute a time based upon a given time and some offset value:
<code>
[juckins@lightning: ~]$ date --date="sat nov 19 2011 6:00pm"
Sat Nov 19 18:00:00 EST 2011

[juckins@lightning: ~]$ date --date="sat nov 19 2011 6:00pm 1 hours 1 minutes"
Sat Nov 19 19:01:00 EST 2011

[juckins@lightning: ~]$ date --date="sat nov 19 2011 6:00pm -1 hours -1 minutes"
Sat Nov 19 16:59:00 EST 2011

$date --date="yesterday 08:00 gmt" '+%y%m%d/%H%M'
121002/0800

$ date --date="today 18:00 gmt" '+%y%m%d/%H%M'
121003/1800

$ date --date="yesterday 08:00 edt" '+%y%m%d/%H%M'
121002/1200

$ date -d @1446390000
Sun Nov  1 15:00:00 UTC 2015
</code>

Converting from seconds and a different timezone:
  TZ=":US/Eastern" date -d @1651335000
  TZ=":America/Phoenix" date -d @1651335000
  TZ=":America/Phoenix" date --date='2022-05-04T14:00:00.000Z'