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    perl -ne 'push @a, $_; $h{$_}++; END{print grep {not --$h{$_}} @a}
+' file

    cabbage
    apple
...
    pear
    banana
    apple

    cabbage
    carrot
...
    pear
    banana
    apple

    perl -ne 'print unless $h{$_}++' file

    sort -u file
    sort file | uniq