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Converting and Formatting System Time

By Will Bontrager

The system time is a number composed of 1 to 10 digits.

The Perl script below converts system time numbers to a human readable date/time string. The system time number 1234567890 converts to Friday, February 13, 2009 at 04:31:30 PM, for example.

The largest system time numbers current Unix/Linux operating systems can work with is 2147483646 (Monday, January 18, 2038 at 08:14:06 PM). That's when time stops :)

Here is the script (about a hundred lines).

#!/usr/bin/perl
use strict;
my %In = ();

sub Parse
{
   my $buffer;
   read(STDIN,$buffer,$ENV{CONTENT_LENGTH});
   for(split /&/,$buffer)
   {
      $_ =~ tr/+/ /;
      my ($n,$v) = split(/=/,$_,2);
      $v =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
      $In{$n} = $v;
   }
} # sub Parse

sub FormattedDateFormat
{
   my($t,$format) = @_;
   if($t =~ /\[/ and $format !~ /\[/) { ($t,$format) = ($format,$t); }
   $t =~ s/\D//g;
   $t = time unless $t > 0;
   $format = '[[WEEKDAY]], [[MONTH]] [[DAY1]], [[YEAR4]]' unless $format =~ /\[/;
   my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($t);
   my @weekday = qw(Sunday Monday Tuesday Wednesday Thursday Friday Saturday);
   my @wkdy = qw(Sun Mon Tue Wed Thu Fri Sat);
   my @month = qw(January February March April May June July August September October November December);
   my @mon = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);
   my ($wkdy,$weekday) = (substr($weekday[$wday],0,3),$weekday[$wday]);
   my $day1 = $mday;
   my $day2 = $mday < 10 ? "0$mday" : $mday;
   my ($mnth,$month) = (substr($month[$mon],0,3),$month[$mon]);
   $mon++;
   my $mon1 = $mon;
   my $mon2 = $mon < 10 ? "0$mon" : $mon;
   $year += 1900;
   my ($year2,$year4) = (substr($year,2),$year);
   $format =~ s/\[\[WKDY\]\]/$wkdy/g;
   $format =~ s/\[\[WEEKDAY\]\]/$weekday/g;
   $format =~ s/\[\[DAY1\]\]/$day1/g;
   $format =~ s/\[\[DAY2\]\]/$day2/g;
   $format =~ s/\[\[MNTH\]\]/$mnth/g;
   $format =~ s/\[\[MONTH\]\]/$month/g;
   $format =~ s/\[\[MON1\]\]/$mon1/g;
   $format =~ s/\[\[MON2\]\]/$mon2/g;
   $format =~ s/\[\[YEAR2\]\]/$year2/g;
   $format =~ s/\[\[YEAR4\]\]/$year4/g;
   return $format;
} # sub FormattedDateFormat

sub FormattedTimeFormat
{
   my($t,$format) = @_;
   if($t =~ /\[/ and $format !~ /\[/) { ($t,$format) = ($format,$t); }
   $t =~ s/\D//g;
   $t = time unless $t > 0;
   $format = '[[HOUR2]]:[[MIN2]]:[[SEC2]] [[APM]]' unless $format =~ /\[/;
   my ($sec,$min,$hour,$mday,$mon,$yr,$wday,$yday,$isdst) = localtime($t);
   if($format =~ /\[\[APM\]\]/)
   {
      if($hour > 11) { $format =~ s/\[\[APM\]\]/PM/g; }
      else           { $format =~ s/\[\[APM\]\]/AM/g; }
      $hour -= 12 if $hour > 12;
   }
   my $hour2 = $hour < 10 ? "0$hour" : $hour;
   my $min2  = $min  < 10 ? "0$min"  : $min;
   my $sec2  = $sec  < 10 ? "0$sec"  : $sec;
   $format =~ s/\[\[HOUR2\]\]/$hour2/g;
   $format =~ s/\[\[HOUR\]\]/$hour/g;
   $format =~ s/\[\[MIN2\]\]/$min2/g;
   $format =~ s/\[\[MIN\]\]/$min/g;
   $format =~ s/\[\[SEC2\]\]/$sec2/g;
   $format =~ s/\[\[SEC\]\]/$sec/g;
   return $format;
} # sub FormattedTimeFormat

sub Convert
{
   my $t = shift;
   return unless $t > 0;
   my $date = FormattedDateFormat $t;
   my $time = FormattedTimeFormat $t;
   return "$date at $time";
} # sub Convert

Parse;
my $datetime = ($In{timestring} > 0 and $In{timestring} < 2147483647) ? Convert $In{timestring} : '';
# January 18, 2038 (2147483646) is last day
print "Content-type: text/html\n\n<html><body>";
print "<h3>$datetime</h3>" if $datetime;
print <<FORM;
<form action="systemtime.cgi" method="POST">
<input type="text" name="timestring" size="15" value=$In{timestring}>
<input type="submit" value="Convert digits to time">
</form>
</body>
</html>
FORM

Almost all of the above script is concerned with formatting.

A default format is used because none is provided. Other formats can be specified.

It's one of the code snippets I keep handy for pasting into projects.

Probably I should make another post about formatting time and date strings. I'll do that sometime.

December 3, 2005

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Converting and Formatting System Time

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Converting and Formatting System Time

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