Bug in Perl script

[vsityz]

I have a script that runs the ptail command with an open descriptor. After 30 seconds, I close the descriptor. But the descriptor is not closed. When the script is closed the tail is present in ps aux.

$log_file = path_to_log;
eval {
   local $SIG{ALRM} = sub { die; };
   alarm (30);
   open (LOG, "tail -F $log_file|") || die "Сan`t open logfile \"$log_file\"";
   while (<LOG>) {
       ***
   }
   alarm (0);
};
close (LOG);
print ("Ok\n");
exit(0);

This code is working well in FreeBSD 8.2, but in FreeBSD 9.0 it's not working.

--
Best Regards
Alexander

 

[SirDice]

My guess is that tail never quits because it doesn't receive an EOF.

This may be helpful: Perfaq5: How do I do a tail -f in perl?

 

[Alt]

I think there is no such glob LOG outside eval block so your close ignored.
Anyway better if you dont use external programs in your script, so SirDice's suggestion is better

 

[anomie]

I think there is no such glob LOG outside eval block so your close ignored.

Good catch.

@vsityz: You really need to have this pragma if you're going to be writing Perl:

use warnings ]

 

[SirDice]

@vsityz: You really need to have this pragma if you're going to be writing Perl:

use warnings ;

You'll want to use

use strict;

too.

 

[fluca1978]

I definitely would say to include strict in every script!
Moreover, it would be interesting to test your script against perlcritic, which could have provided a good guess:

Return value of "close" ignored at line 11, column 1.  Check the return value of "close" for success.  Severity: 2

 

[vsityz]

I have rewritten this code:

eval {
      local $SIG{ALRM} = sub { die };
      alarm ($rtime);
      open (LOG, "$log_file") || die "error open logfile \"$log_file\"";
      seek (LOG, 0, 2);
      for (;;) {
         for ($curpos = tell(LOG); <LOG>; $curpos = tell(LOG)) {
              . . .
         }
         sleep (1);
         seek (LOG, $curpos, 0);
      }
      alarm (0);
      close (LOG);
};

This works well.

 

[serverhamster]

Instead of strict and warnings, you can also use common::sense. It can be found in devel/p5-common-sense.

 

[estrabd]

You should also be using the 3-parameter open with a variable $FH, not a bare one (LOG).

 

[estrabd]

I have a script that runs the ptail command with an open descriptor. After 30 seconds, I close the descriptor. But the descriptor is not closed. When the script is closed the tail is present in ps aux.

$log_file = path_to_log;
eval {
   local $SIG{ALRM} = sub { die; };
   alarm (30);
   open (LOG, "tail -F $log_file|") || die "Сan`t open logfile \"$log_file\"";
   while (<LOG>) {
       ***
   }
   alarm (0);
};
close (LOG);
print ("Ok\n");
exit(0);

This code is working well in FreeBSD 8.2, but in FreeBSD 9.0 it's not working.

--
Best Regards
Alexander

More on style:

The proper way to catch errors inside of an eval is to do something like:

my $eval_ok = do { local $@; eval { ... || die; } };
if (!$eval_ok) {
  # handle failure
} 
#else { .. }

You should also give Try::Tiny a look.

 

[Alt]

The proper way to catch errors inside of an eval is to do something like:

I'd say it should be like

my $eRes = eval {
   ...;
   return 1;
};
unless( $eRes ) {
   ...;
}

Or maybe more simple variant:

eval {
   ...;
   return 1;
} || do {
   ...;
}

This cus some errors can put "0" or "" into $@ variable. Already got this kind of problem with DBI exceptions

 

[estrabd]

One minor nit; in:

eval {
   ...;
   return 1;
} || do {
   ...;
}

I've recently learned to appreciate the extra-low precedence 'or'.

eval {
   ...;
   return 1;
} or do {
   ...;
}