$ sudo qm guest exec 200 -- ls /etc/hosts /swap.img | jq .
{
  "err-data": "ls: cannot access '/swap.img': No such file or directory\n",
  "exitcode": 2,
  "exited": 1,
  "out-data": "/etc/hosts\n"
}
$ sudo qm guest exec 200 -- ls /etc/hosts /swap.img | jq --raw-output '.["err-data"]'
ls: cannot access '/swap.img': No such file or directory
$ sudo qm guest exec 200 -- ls /etc/hosts /swap.img | jq --raw-output '.["out-data"]'
/etc/hosts