sub shell_quote {
    my $s = @_ ? $_[0] : $_;
    return $s if $s =~ /^[a-zA-Z0-9-_]+\z/;
    $s =~ s/'/'\\''/g;
    return "'$s'";
}

my $server  = 'localhost';
my $cmd     = 'ls -ltra';
my $timeout = 3;

my $watchdog = <<'__EOI__';
    $t = shift;
    $SIG{ALRM} = sub { kill INT => $p };
    exec(@ARGV) unless $p = fork;
    alarm $t;
    waitpid $p, 0
    #exit(...)
__EOI__

my $watchdog_cmd = join ' ', map shell_quote,
    perl => "-e$watchdog", $timeout, $cmd;

my $ssh_cmd = join ' ', map shell_quote,
    ssh => $server, $watchdog_cmd;

my $output = `$ssh_cmd`;