arp -a | perl -MData::Dump -anE '$F[1]=~s/(?:\)|\()//g;$h{$F[1]}=$F[3]}{dd\%h'
{
  "172.31.219.36" => "00:ae:da:23:85:d0",
  "192.168.1.1"   => "48:f8:b3:3c:30:33",
  "192.168.1.115" => "70:77:81:43:ae:ab",
  "192.168.1.138" => "84:38:38:9b:61:64",
  "192.168.1.140" => "00:ac:1a:61:0e:66",
  "192.168.1.143" => "<incomplete>",
  "192.168.1.4"   => "<incomplete>",
}