Death of sleep?

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

I am attempting to create a loop that will perform a function every $interval seconds. When I attempt to use the sleep function, the first line of the loop that I have create isn't executed. Without further ado, the code loop:

#!/usr/bin/perl -w

my $interval=5;

LOOP: {
    print STDOUT "test"; #used STDOUT here, just to be sure
    sleep ($interval);
    redo LOOP;
}
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Different variations of for(;;) while(), etc have also been tried with no success.

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Re: Death of sleep? by clintp (Curate) on Aug 08, 2001 at 18:13 UTC
You are suffering from buffering. Try: `$\|=1` near the beginning of your program, or pick a file descriptor like STDERR that doesn't have this problem. More information in the FAQ...	[reply] [d/l]
Re: Death of sleep? by trantor (Chaplain) on Aug 08, 2001 at 18:16 UTC
`STDOUT` is buffered, this means that no actual output will be written until the buffer is full or there's a newline. If you `print "test\n";` or if you set the `$\|` variable to nonzero (e.g. with `$\|++;` or with `$\| = 1;`), you'll get what you want. Setting `$\|` to a nonzero value disables buffering. Technically, it flushes it every time you write (to `STDOUT`, in your case). May I also suggest you to rework your simple loop? I know it's just a test, but it looks a bit weird: there's no need for `redo` and labels in this simple case, so I'd suggest you to use the variations you mentioned in your post. Happy learning! -- TMTOWTDI	[reply] [d/l] [select]
Re: Death of sleep? by Zaxo (Archbishop) on Aug 08, 2001 at 18:15 UTC
Your code works if you set `$\|=1;` before LOOP. That autoflushes the prints rather than waiting till STDOUT is closed ( too late then ;-). After Compline, Zaxo	[reply] [d/l]
Re: Death of sleep? by John M. Dlugosz (Monsignor) on Aug 08, 2001 at 18:16 UTC
Add the line `$\|=1;` to the top of your script, “to make your pipes piping hot!”. The print is being executed, but the buffer isn't flushed. —John	[reply] [d/l]