my $N = 10;    # timeout in seconds
my $out;       # read into here

# See Perl Cookbook 2nd edition, Recipe 16.21
# See also perlfaq8 "How do I timeout a slow event".
# Read a chunk from file handle <COM>, timing out after $N seconds.
# Return number of bytes read, 0 if EOF, -1 if timed out.
sub read_for {
   my $diestr = 0;
   my $nbytes = 0;
   eval {
      local $SIG{ALRM} = sub { die "alarm clock restart" };
      alarm($N);    # schedule alarm in $N seconds
      eval {
         $nbytes = sysread(COM, $out, 1024);
      };
      $diestr = $@ if $@;
      alarm(0);           # cancel the alarm
   };
   $diestr = $@ if $@;
   alarm(0);              # race condition protection
   return $nbytes unless $diestr;
   return -1 if $diestr =~ /alarm clock restart/;
   die $diestr;
}

while (1) {
   my $nbytes = read_for();
   if ($nbytes < 0) {
      print "timed out after $N seconds\n"; last;
   } elsif ($nbytes == 0) {
      print "eof\n"; last;
   }
   print "chunk='$out'\n";
}