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

    cabbage
    apple
    banana
    grape
    pear
    banana
    carrot
    apple
    apple
    banana
    grape
    pear
    banana
    apple
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The output would be:

    cabbage
    carrot
    grape
    pear
    banana
    apple
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So for example the last instance of apple is printed instead of the first. For comparison try the following which leaves the first instance in place:

    perl -ne 'print unless $h{$_}++' file
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If preserving order isn't important then you could use other system commands (if supported):

    sort -u file
    sort file | uniq
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Note: this snippet potentially stores 2 copies of each line in memory so it is inefficient for large files.