Perl Daemon Not Working with Sleep()

Question

I wrote a simple test daemon using Proc::Daemon . Here is the daemon:

 #!/usr/bin/perl

 use Proc::Daemon;

 $daemon = Proc::Daemon->new(
        work_dir     => '/scripts/',
        child_STDOUT => '/scripts/child.log',
        child_STDERR => '+>>debugchild.txt',
        pid_file     => 'pid.txt',
        exec_command => 'perl /scripts/test.pl'
    );


foreach(@ARGV)
{
if ( /install/i )
{
    $Kid_1_PID = $daemon->Init;
}
elsif (/remove/i)
{
    $stopped = $daemon->Kill_Daemon();
}
}

And here is test that it executes:

#!/usr/local/bin/perl

while (1) {

print "test\n";
sleep(1);
}

The while loop works fine with just the print statement, but when I add sleep(); the log is empty. Why would this be?

ADW · Accepted Answer · 2011-06-22T15:54:04.863

5

Perl will not automatically flush the buffer so your write to the file will only happen after quite a while. When you don't have the sleep your buffer will be almost automatically flushing due to the volume of data being written.

Try this:

$| = 1;
while (1) {
    print "test\n";
    sleep(1);
}

edited Jun 22 '11 at 15:54

answered Jun 22 '11 at 15:46

ADW

4,030
17
13

Can you explain what $| = 1 does? – HighLife Jun 22 '11 at 15:59
It tells Perl to flush the buffer after each write rather than waiting until there are enough bytes in the buffer to send it to a file. – ADW Jun 22 '11 at 16:03

mob · Answer 2 · 2011-06-22T15:50:59.053

4

Output buffering and not enough patience? With a sleep(1) in the loop, it could take a while for enough data to accumulate and be flushed to the log file.

Put a $|=1; statement at the top of your script.

edited Jun 22 '11 at 15:50

answered Jun 22 '11 at 15:45

mob

117,087
18
149
283

score 0 · Answer 3 · answered Aug 07 '20 at 14:26

0

you can also use:

to flush the print on console:

select()->flush();

to flush in to the file with the fileHandle $FH

$FH->autoflush;

answered Aug 07 '20 at 14:26

Aravind Nadumane

170
1
11

Perl Daemon Not Working with Sleep()

3 Answers3

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