在PID中用perl尾部文件

Question

I have a requirement to check a log file till a PID is alive in perl. It is working fine in bash.

tail -f --pid=1234 logfile.log

Now I need the same to do with perl to check a log file either by checking the PID or giving the time interval also works for me.

I am using the following code to do it in perl, but I am able to tail a file and have two issues in it.

1) Tail of a file is not happening immediatly.

2) I want to close the tail after few seconds, say 100.

use warnings;
use strict;
use File::Tail; 
my $name='/tmp/out'; 
my $file=File::Tail->new(name=>$name,interval=>1,maxinterval=>5,adjustafter=>1);
my ($found,$timeleft,@pending) = File::Tail::select(undef,undef,undef,100,$file);

if ($found)
{
   print $pending[0]->read;
}

I am using the above code and it is exiting in only 2 seconds. I am looking for to tail a file like exactly tailf command in linux to exit after the time given.

Thanks.

Answer 1

From the documentation :

The module tries very hard NOT to "busy-wait" on a file that has little traffic. Any time it reads new data from the file, it counts the number of new lines, and divides that number by the time that passed since data were last written to the file before that. That is considered the average time before new data will be written. When there is no new data to read, File::Tail sleeps for that number of seconds. Thereafter, the waiting time is recomputed dynamicaly. Note that File::Tail never sleeps for more than the number of seconds set by maxinterval.

So you need to set maxinterval to a low number if you want it to see updates immediately.

Update: to timeout, use select . This simple example does a single, 100-second check on the file. It also checks the file at least every five seconds. For a more complex example using a loop, see the aforementioned documentation.

use warnings;
use strict;
use File::Tail; 
my $name='/tmp/out'; 
my $file=File::Tail->new(name=>$name,interval=>1,maxinterval=>5,adjustafter=>1);
my ($found,$timeleft,@pending) = File::Tail::select(undef,undef,undef,100,$file);

if ($found)
{
   print $pending[0]->read;
}

Update: here is a looping solution that will keep going for your entire time interval:

use warnings;
use strict;
use File::Tail; 
my $name='/tmp/out'; 
my $file=File::Tail->new(name=>$name,interval=>1,maxinterval=>5,adjustafter=>1);

my $time = 60;

while ($time > 0)
{
    my ($found,@pending);
    ($found,$time,@pending) = File::Tail::select(undef,undef,undef,$time,$file);

    if ($found)
    {
        print $_->read for @pending;
    }
}