use strict;
use warnings;

use IO::Select  qw( );
use IPC::Open2  qw( open2 );
use Time::HiRes qw( time );   # Optional

my $timeout    = 30.000;   # Abort after this many seconds.
my $command    = '...';    # The command to execute.
my $from_child = '';       # Receives the output of the command.

my $pid = open2(undef, my $fh_from_child, $command);
my $sel = IO::Select->new($fh_from_child);
my $abort_time = time + $timeout;
for (;;) {
   my $time_left = $abort_time - time;
   my @r = $time_left > 0 ? $sel->can_read($time_left): ();
   if (!@r) {
      kill(TERM => $pid);
      die("Child took more than $timeout seconds.\n");
   }

   read($fh_from_child, $from_child, 4096, length($from_child))
      or last;
}

print($from_child);

waitpid($pid, 0);