where did you assigned value to $pid ? :-)
You can also miss some data, for example @cmd can handle TERM signal and print partial result. @cmd also can block/not handle TERM signal (or in some case, cannot be KILLed).
Sample:
use strict;
use warnings;
use IO::Pipe;
use constant TIMEOUT => 5;
my @cmd = ();
my $pipe = new IO::Pipe;
if (my $pid = fork) {
$pipe->reader;
$SIG{ALRM} = sub {
kill TERM => $pid;
$SIG{ALRM} = sub {
kill KILL => $pid;
$SIG{ALRM} = sub { close $pipe; };
alarm TIMEOUT;
};
alarm TIMEOUT;
};
$SIG{CHLD} = sub {
while (my $wait = wait) {
alarm 0 if $wait == $pid;
}
};
# alarm here if you want force child to quit after TIMEOUT
# alarm TIMEOUT;
while (my $from_child = <$pipe>) {
# alarm here if you want to interrupt child after inactivity
# (no output lines)
# alarm TIMEOUT;
# ...
};
alarm (0);
close $pipe;
} elsif (defined $pid) {
# Child
$pipe->writer;
open STDOUT, '>&', $pipe;
exec @cmd;
} else {
die "Fork failed: $!\n";
}