my @cmd = (cat => (
    '/etc/passwd',
));

my @sshcmd = ('/usr/bin/ssh' => (
    -t => (),
    -i => "$HOME/.ssh/mypubkey",
    -o => 'StrictHostKeyChecking no',
    'user@host',
    @cmd
));

open(my $fr_ssh, '-|', @sshcmd)
    or die("Can't fork and pipe: $!\n");