Fuism has asked for the wisdom of the Perl Monks concerning the following question:

Hi experts, I have created my own program to add and subtract (in this example Im subtraction 7 days from current day so basically a week ago) calendar dates. Is there an easier way to do this without having to update the code (in my validate_years and validate_month subs). It works but Im still unconfident about the outcome. Sorry the code is so long. Any advice would be appreciated. Thanks in advance... Fue 
#!/usr/bin/perl

#Variables for dates
$year = qx(date +%Y);
$month = qx(date +%b);
$date = qx(date +%d);
$date2 = $date;
$month = uc($month);
chop($month);
chop($date);
chop($date2);
chop($year);

#Opens template and write to SAS file to use
die("Cannot open daily_pull_temp.sas to write to.")
     unless(open(WRITE, ">daily_pull_temp.sas"));
 
die("Cannot open daily_pull.sas to read from.")
     unless(open(GETDATA, "<daily_pull.sas"));
while($get = <GETDATA>) {
    if ($get =~ /<date2>/) {
        $get =~ s/<date2>/$date2/g;
    }
     if ($get =~ /<year><month>/) {
        if ($date <= 7) {
            $month = &minus_month($month);
               $newdate = &validate_Month($month);
            $date = ($newdate + $date); 
            $date = $date - 7;
#             $year = &validate_Year($month);
            $month = &change_mo2num($month);
            $get =~ s/<year>/$year/g;
            $get =~ s/<month>/$month/g;
            $get =~ s/<date>/$date/g;
            print WRITE "$get";
          } 
          else {
               #month stays as current month
               $newdate = &validate_Month($month);
#                $year = &validate_Year($month);
               $month = &change_mo2num($month);
            $date = $date - 7;
            if ($date < 10) {
                $date = "0" . $date;
            }
               $get =~ s/<year>/$year/g;
            $get =~ s/<month>/$month/g;
            $get =~ s/<date>/$date/g;
            print WRITE "$get";
          }
     }
    else {    
        print WRITE "$get";
    }
}
close(WRITE);
close(GETDATA);

###### SUBS START HERE ###############

sub validate_Year {
    my ($month) = @_;
    if ($month eq "jan") {
          $yr = qx(date +%Y);
          return $yr;
     }
     else {
          ####### Must Change #######
          $yr = "2003";
     }
}
 

sub validate_Month {
    my ($m) = @_;
     if (($m eq "JAN") xor($m eq "MAR") xor ($m eq "MAY") xor
     ($m eq "JUL") xor ($m eq "AUG") xor ($m eq "OCT") xor
     ($m eq "DEC")) {
           $day = 31;
           return $day;
     }
     elsif (($m eq "APR") xor($m eq "JUN") xor ($m eq "SEP") xor
     ($m eq "NOV")) {
          $day = 30;
          return $day; 
     }
     elsif ($m = "FEB") {
         if (($testyear eq "2003") xor ($testyear eq "2005") xor ($tes
+tyear eq "2007")
          xor ($testyear eq "2009")) {
               $day = 28;
               return $day;
          }
          else {
               $day = 29;
               return $day;
          }
     }
}
 
 
 
sub add_month {
    my ($month) = @_;
    if ($month eq "JAN") {
          $month = "FEB";
          return $month;
     }
     elsif ($month eq "FEB") { 
          $month = "MAR";
          return $month;
     }
     elsif ($month eq "MAR") { 
          $month = "APR";
          return $month;
     }
     elsif ($month eq "APR") {
          $month = "MAY";
          return $month;
     }
     elsif ($month eq "MAY") {
          $month = "JUN";
          return $month;
     }
     elsif ($month eq "JUN") {
          $month = "JUL";
          return $month;
     }
     elsif ($month eq "JUL") {  
          $month = "AUG";

          return $month;
     }
     elsif ($month eq "AUG") { 
          $month = "SEP";
          return $month;
     }
     elsif ($month eq "SEP") {
          $month = "OCT";
          return $month;
     }
     elsif ($month eq "OCT") {
          $month = "NOV";
          return $month;
     }
     elsif ($month eq "NOV") {
          $month = "DEC";
          return $month;
     }
     elsif ($month eq "DEC") {
          $month = "JAN";
          return $month;
     }
}


sub minus_month {
    my ($month) = @_;
     if ($month eq "JAN") {
          $month = "DEC";
          return $month;
     }
     elsif ($month eq "FEB") { 
          $month = "JAN";
          return $month;
     }
     elsif ($month eq "MAR") { 
          $month = "FEB";
          return $month;
     }
     elsif ($month eq "APR") {
          $month = "MAR";
          return $month;
     }
     elsif ($month eq "MAY") {
          $month = "APR";
          return $month;
     }
     elsif ($month eq "JUN") {
          $month = "MAY";
          return $month;
     }
     elsif ($month eq "JUL") {  
          $month = "JUN";
          return $month;
     }
     elsif ($month eq "AUG") { 
          $month = "JUL";
          return $month;
     }
     elsif ($month eq "SEP") {
          $month = "AUG";
          return $month;
     }
     elsif ($month eq "OCT") {
          $month = "SEP";
          return $month;
     }
     elsif ($month eq "NOV") {
          $month = "OCT";
          return $month;
     }
     elsif ($month eq "DEC") {
          $month = "NOV";
          return $month;
     }
}
 
#The 2 subroutines for date conversion
sub change_num2mo{
    my ($month) = @_;
    if ($month =~ /01/) {
          $num_month = "jan";
          return $num_month;
     }
     if ($month =~ /02/) {
          $num_month = "feb";
          return $num_month;
     }
     if ($month =~ /03/) {
          $num_month = "mar";
          return $num_month;
     }
     if ($month =~ /04/) {
          $num_month = "apr";
          return $num_month;
     }
     if ($month =~ /05/) {
          $num_month = "may";
          return $num_month;
     }
     if ($month =~ /06/) {
          $num_month = "jun";
          return $num_month;
     }
     if ($month =~ /07/) {
          $num_month = "jul";
          return $num_month;
     }
     if ($month =~ /08/) {
          $num_month = "aug";
          return $num_month;
     }
     if ($month =~ /09/) {
          $num_month = "sep";
          return $num_month;
     }
     if ($month =~ /10/) {
          $num_month = "oct";
          return $num_month;
     }
     if ($month =~ /11/) {
          $num_month = "nov";
          return $num_month;
     }
     if ($month =~ /12/) {
          $num_month = "dec";
          return $num_month;
     }
}

sub change_mo2num {
    my ($month) = @_;
     if ($month =~ /JAN/) {
          $num_month = "01";
          return $num_month;
     }
     if ($month =~ /FEB/) {
          $num_month = "02";
          return $num_month;
     }
     if ($month =~ /MAR/) {
          $num_month = "03";
          return $num_month;
     }
     if ($month =~ /APR/) {
          $num_month = "04";
          return $num_month;
     }
     if ($month =~ /MAY/) {
          $num_month = "05";
          return $num_month;
     }
     if ($month =~ /JUN/) {
          $num_month = "06";
          return $num_month;
     }
     if ($month =~ /JUL/) {
          $num_month = "07";
          return $num_month;
     }
     if ($month =~ /AUG/) {
          $num_month = "08";
          return $num_month;
     }
     if ($month =~ /SEP/) {
          $num_month = "09";
          return $num_month;
     }
     if ($month =~ /OCT/) {
          $num_month = "10";
          return $num_month;
     }
     if ($month =~ /NOV/) {
          $num_month = "11";
          return $num_month;
     }
     if ($month =~ /DEC/) {
          $num_month = "12";
          return $num_month;
     }
}

[download]

Replies are listed 'Best First'.
Re: adding/subtracting calender dates
by tlm (Prior) on Jun 02, 2005 at 19:00 UTC

    I haven't read your code (which, BTW, you should put between <readmore></readmore> tags), but it looks to me like you are re-inventing a thoroughly invented wheel. Look at Date::Calc, for example.

    the lowliest monk

[reply]
      Thanks guys... Duh, why didnt I think of that.. Anyways I tried the readmore, I just forgot the /readmore... Sorry guys... I will take all ur advice and try the date modules. Everyone gets Votes for being alot smarter than me... :)
[reply]
Re: adding/subtracting calender dates
by ysth (Canon) on Jun 02, 2005 at 19:02 UTC
    A good way to comfort yourself is to design some tests, but in this case, you are laboriously reinventing a wheel that's likely to leave you with buggy code. Try DateTime or Date::Manip or Date::Calc.

    By the way, I don't think xor does what you think it does.

[reply]
      Hmmm well it seemed to work like I wanted. Please let me know what you think it does. It would be great to know what it really does as to what I think it does. Thanks again... Fue
[reply]
      xor =
      by hubb0r (Pilgrim) on Jun 02, 2005 at 20:50 UTC
        FYI - xor is an "exclusive or". It has the following rules: 
        (1 xor 1) == 0
(1 xor 0) == 1
(0 xor 1) == 1
(0 xor 0) == 0
(0 xor 1 xor 1) == 0
(0 xor 1 xor 0) == 1
etc etc

        [download]
        Meaning that it will return true if and only if exactly 1 of the xor'd variables returns true.
[reply]
[d/l]
Re: adding/subtracting calender dates
by kirbyk (Friar) on Jun 02, 2005 at 19:13 UTC
    First off, there are some perl modules that do all of this stuff for you. Date::Calc and Date::Manip are both good starts. (I'm sure someone will have posted links before I finish typing this.)

    But, in the interest of learning a programming trick or two, though, consider doing your month math something more like: 

    my @months = qw(JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC);

sub change_num_to_month {
     my $num_month = shift;
     return $months[$num_month - 1];
}

sub add_month {
    my $month = shift;
    my $month_num = change_month_to_num($month);
    $month_num++;
    $month_num = 1 if $month_num > 12;
    return change_num_to_month($month_num);
}

# And very similarly for subtract month

    [download]
    Getting the reverse lookup is slightly trickier. I'd probably convert the array into a hash, something like: (I'm sure you can do better with a map, but let's go for readibilty first.) 
    my %month_nums;
for (my $i = 0; $i <= $#months; $i++) {
   $month_nums{$month[$i]} = $i;
}

# This creates a hash of 'Jan' => 0, 'Feb' => 1, etc.

sub change_month_to_num {
    my $month = shift;
    return $month_nums{$month} + 1;
}

    [download]
    One has to be careful about the array index starting at 0, if you want your month nums to range from 1 to 12, but that's the only really tricky bit.

    -- Kirby, WhitePages.com

[reply]
[d/l]
[select]
Re: adding/subtracting calender dates
by fishbot_v2 (Chaplain) on Jun 02, 2005 at 19:19 UTC

    In addition to agreeing with the previous posters that there are excellent modules out there that solve this problem better, I have a general comment about your code:

    Any time you have that many if-elses or ifs in a row, program your brain to think of either a loop, or a hash, or both. Your month-to-num and the reverse could have been implemented better with an array or hash-reversed solution. Adding to month can then be a switch to a number, then a normal add, then a switch back, etc.

    I can't make any sense out of the validate_Month subroutine... (it returns days? why? And the leap year code is mystifying...) but that would be a lot easier with a hash.

    Not for this code, which should be replaced with an existing module, but for next time.

[reply]
[d/l]
Re: adding/subtracting calender dates
by dave0 (Friar) on Jun 02, 2005 at 19:01 UTC
    You should really have a look at Date::Calc instead.
[reply]
Re: adding/subtracting calender dates
by TedPride (Priest) on Jun 02, 2005 at 21:01 UTC
    Pardon me for asking stupid questions, but what's wrong with timestamps and localtime()? For instance, to get the date / time of 7 days ago: 
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(t
+ime() - 7*86400);

    [download]
    If you're going to give an example of what your code can do, it needs to be something that can't be achieved just as easily using built-in Perl functions.
[reply]
[d/l]
      It would require some care during DST change, because one day would last a hour more/less.

      Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))')

      Don't fool yourself.
[reply]

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