Wire64 has asked for the wisdom of the Perl Monks concerning the following question:

Hi wisdom monks,
Im trying to write someting that will a number of display messages based on systemclock, ill try to explain.

Say i got 10 messages and i want to show one every 5 seconds. so 1 message shows when the time is between 0:00 and 0:04seconds;
2nd message will show 0:05 <-> 0:09 seconds. ... message 10 will show 0:45 <-> 0:49.
then message 1 will show again from 0:50 <-> 0:54. 2 will be 0:55 <-> 0:59
when minute 1 starts i want it to start with message 3, thats 1:00 <-> 1:04
My question is how do i calculate this :)
hope this makes sence, thanks in advanced,
Wire64

dont have much that will do the above but will show you where i'am at now. 

#!/usr/bin/perl
#
# display stuff on systemclock

use Switch;

# Get current date & time
my ($tsec,$tmin,$thour,$tday,$tmonth,$tyear,$twday,$tyday,$tisdst) = l
+ocaltime(time);

$showitems=10;
$delay=5;

$totalshowtime=$showitems*$delay;

#calulate how many minutes it will take to complete
$showminutes = $totalshowtime / 60;

#remove everthing behind the . so we get a round number
$showminutes =~ s/(\d)\.\d*/$1/;

switch ($showminutes) {
        case /0/ {
        my $number= $tsec / ($showitems * $delay) ;
        print "$number\n";
        #print "0\n";
        }

        case /1/ {print "1\n";
        }
else {print "-$showminutes- did not match any\n";}
}

print "$showminutes | $totalshowtime =  $showitems * $delay";
print "\n$tsec $tmin";

[download]

Replies are listed 'Best First'.
Re: display stuff based on systemclock
by ikegami (Patriarch) on Jul 09, 2009 at 15:55 UTC

    Something like this? 

    my @mesages = (...);

my $pass = 0;
for my $message (@messages) {
    sleep(5) if !$pass++;
    print($message);
}

    [download]

    sleep is interruptible and drift can occur if the loop body is non-trivial, so maybe the following would be better: 

    use Time::HiRes qw( time sleep );  # Optional

sub sleep_until {
    my ($e_time) = @_;
    for (;;) {
        my $dur = $e_time - time;
        last if $dur <= 0;
        sleep($dur);
    }
}

my @mesages = (...);

my $s_time = time;
for my $i (@messages) {
    sleep_until($s_time + 5*$i);
    print($message);
}

    [download]
[reply]
[d/l]
[select]
      no i dont want it to use sleep, i want the program to exit after displaying the message.
      So when i execute the program at 7:05:02 i get a message and if i execute the program at 7:05:06 i get the next message. Should have explained that sorry. and i dont want to write to disk either.
[reply]
        Forgetting we're dealing with times for a second, that's usually done using by subtracting the remainder of a division by your slot size. 
        $ perl -e'printf "%-3s %2d\n", "$_:", $_ - ($_ % 5) for 0..19'
0:   0
1:   0
2:   0
3:   0
4:   0
5:   5
6:   5
7:   5
8:   5
9:   5
10: 10
11: 10
12: 10
13: 10
14: 10
15: 15
16: 15
17: 15
18: 15
19: 15

        [download]

        The same trick can be applied to times. 

        $ perl -MPOSIX -le'@lt = localtime; $lt[0] -= $lt[0] % 5; print strfti
+me "%Y-%m-%dT%H:%M:%S", @lt'
2009-07-09T12:14:40

$ perl -MPOSIX -le'@lt = localtime; $lt[0] -= $lt[0] % 5; print strfti
+me "%Y-%m-%dT%H:%M:%S", @lt'
2009-07-09T12:14:40

$ perl -MPOSIX -le'@lt = localtime; $lt[0] -= $lt[0] % 5; print strfti
+me "%Y-%m-%dT%H:%M:%S", @lt'
2009-07-09T12:14:45

$ perl -MPOSIX -le'@lt = localtime; $lt[0] -= $lt[0] % 5; print strfti
+me "%Y-%m-%dT%H:%M:%S", @lt'
2009-07-09T12:14:45

        [download]

        The question is what do you want to happen if 60 isn't divisible by $delay?

[reply]
[d/l]
[select]
Re: display stuff based on systemclock
by ramlight (Friar) on Jul 09, 2009 at 17:49 UTC
    If I understand your problem correctly, you just want to display one of a number of messages based on the current time, then quit.

    UPDATE: As noted by Ikegami below, this is wrong!
    "So take the current time in seconds; mod it by the total number of seconds in a message cycle, and divide the results by the number of messages you have:"

    The correct formula (Thanks to Ikegami again) is (time / message-display-time) mod number-of-messages. 

    # See correct version of this by ikegami below!
@message = ("Message 1",
            "Message 2",
            "Message 3",
            "Message 4",
            "Message 5",
            "Message 6",
            "Message 7",
            "Message 8",
            "Message 9",
            "Message 10");

$num_msgs = @message;
$msg_time = 5;
$total_time = $num_msgs * $msg_time;

$msg_num = int((time() % $total_time) / $num_msgs);

print $message[$msg_num], "\n";

    [download]
[reply]
[d/l]

      Ah! That's what the OP meant. Unfortunately, there's a bug in your formula.

      It displays the first $msg_time messages for $num_msgs seconds.
      It should display the $num_msgs messages for $msg_time seconds.

      Fixed: 

      my @message = (
    "Message 1",
    "Message 2",
    "Message 3",
    "Message 4",
    "Message 5",
    "Message 6",
    "Message 7",
    "Message 8",
    "Message 9",
    "Message 10",
);

my $msg_time = 5;

print $message[ time / $msg_time % @message ], "\n";

      [download]
[reply]
[d/l]
[select]
        You are, of course, right. A little more time spent verifying my results would definitely have been worth while!
[reply]

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