perl -wlF'\|' -e 'for (@F) { /(\w+)="(\w+)"/; $r{$1} = $2 } 
$x="$r{pet}:$r{hate}"; $s{$x} ? next : ++$s{$x} && print' <input
pet="cat"|hate="rat"|like="dog"
pet="cow"|hate="rat"|like="dog"