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

Hi, I'm trying to write a script that will read a database, check the date in the DB, add X days to that date, compare it with today's date and if the dates match (todays and modfied date from db) then perform a function. If they don't it just needs to move to the next line of the DB. I think the Date::Calc module will do this for me but the documentation is really confusing and I can't figure out how to do what I want. My question is, how do I add X days to one date, match it against today's date and then perform a function if it matches. All help is welcome as I'm pretty stuck! - Neil

Replies are listed 'Best First'.
(jeffa) Re: Date::Calc Module
by jeffa (Bishop) on Dec 29, 2001 at 22:35 UTC
    I like maverick's suggestion better, but here is some code for you to toy with to get the hang of the somewhat hard to get the hang of Date::Calc 
    use strict;
use Date::Calc qw(Add_Delta_YMD Delta_Days);

my $date1 = '2001/12/25/';  # Dec 25, 2001

my ($d,$m,$y) = (localtime)[3..5];
my $today = join('/', $y+1900, $m+1, $d);

# add x days to date1
my $date2 = join('/',
   Add_Delta_YMD(
      split('/',$date1),  # date 1
      0,0,4               # plus 4 days
   )
);


# compare it to today's date
print "same day\n" if Delta_Days(
   split('/',$date2),
   split('/',$today),
) == 0;

    [download]
    I also recommend getting a copy of the Perl Cookbook, chapter 3 is devoted solely to working with dates.

    jeffa 

    L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)
[reply]
[d/l]
      Hi, No matter what I change $date1 to, it returns 'same day'!? - Neil
[reply]
        If you change the day portion, you will not get 'same day'. However, if you change the year or the month without changing the day, you will. The reason is because i chose to compare the dates by the number of days - not the year and/or month.

        Like I said, this is just to get you going.

        jeffa 

        L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)
[reply]
(maverick) Re: Date::Calc Module
by maverick (Curate) on Dec 29, 2001 at 22:24 UTC
    Most databases have date manipulation functions built in. If you're using mysql for example (your database probably has different commands for this) you write your sql query as: 
    SELECT 
    something
FROM
    some_table
WHERE 
    TO_DAYS(NOW()) - TO_DAYS(date_column) = 10;

    [download]
    That would return all the matching rows where date_column is 10 days less that today's date. NOW give you the current date, TO_DAYS converts the date to a number of days so that you can do a subtraction. This would be significantly faster than selecting out every row and then doing the date manipulation stuff in perl.

    HTH (I can provide a more complete example if you want)

    /\/\averick
    perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"

[reply]
[d/l]
      Hi, I'm using a flat-file text db but thanks anyway. :o) - Neil
[reply]
(shockme) Re: Date::Calc Module
by shockme (Chaplain) on Dec 29, 2001 at 22:39 UTC
    maverick's suggestion is definitely the efficient way to go. However, if you still find yourself needing Date::Calc, here's the format to add 5 days to your current date: 

    $NumDays = 5;
($NewYear, $NewMon, $NewYear) = 
     Add_Delta_Days($CurrYear, $CurrMon, $CurrDay, $NumDays);

    [download]

    Update: Doh! jeffa beat me to the punch. And, as usual, he's response is more complete. ++

    If things get any worse, I'll have to ask you to stop helping me.

[reply]
[d/l]
      That did exactly what I need. Thank you! I'd found that code before but got confused with how to use it I think but now i've figured it out! Thanks a lot everyone for all your help! - Neil
[reply]
Date::Calc Alternative
by Jazz (Curate) on Dec 30, 2001 at 08:03 UTC

    I like Class::Date instead of Date::Calc for this kind of simple date math (where sql statements can't be used).

    use Class::Date qw/ date localdate now /;

my $cmpday = date( date( '2001-11-9' ) + '1M' + '20D' ); # add 1 month
+, 20 days
my $today  = date( localdate( now ))->truncate; # truncate makes time 
+midnight.

if ( $cmpday == $today ){
    print "Today is $cmpday.\n";
}
else {
    print +( Class::Date->new( $today ) - $cmpday )->day, " days away.
+\n";
}

    [download]

    Date::Calc is definitely faster, so if you're needing lots of speedy date calcs, stick with Date::Calc. Docs for Class::Date is here.

[reply]
[d/l]
Re: Date::Calc Module
by rbc (Curate) on Dec 30, 2001 at 07:43 UTC
    I would do this in the DBMS.
    Assuming PL/SQL
    procedure foo ( Xday number ) is
    nmatch number := 0;
begin

select count(*) into nmatchs
from Whatever a
where trunc(a.theDBdate + Xday) = trunc(sysdate);

if nmatch > 0 then
     callSomeFunction();
end if; 
end;

    [download]

    This assumes that the function you are calling
    is a stored function, and your DB is oracle and
    well ... it assumes a lot. But I think it is fair
    to ask why not do this with a SQL query?

    I don't know ... sorry if this isn't the
    answer you are looking for but sometimes
    you can't beat a good select statement.

    --
    Its like a dog that can sing and dance.
    It's remarkable because it can do it.
    Not that it can do it well.
[reply]
[d/l]

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