Maybe use Text::ParseWords

#!perl
use strict;
use Text::ParseWords;

while (<DATA>){
  chomp;
  my @parts = quotewords('\s+',0,$_);
  print join "|",@parts,"\n";
}

__DATA__
"my" "dog"
"my" "dog shepherd"
my dog
my "dog shepherd"
"my "dog"
my "dog shepherd
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