I think you can use your original design. Please do not match quotes in quotes.

  my @quotes = $keyword =~ s/"([^"]*)?"//;
  my @keys = split(/ /, $keyword);
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If you think about spaces at the end or two spaces in the middle modify your code like

 
  my @keys =grep length, split(/ /, $keyword);
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or

 
  my @keys = split(" ", $keyword);
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