Well, one problem you're having is context confusion:

perl -e 'sub foo {@a=(1,2,4);return @a};
$bar=foo();
print "bar is $bar\n";'

bar is 3
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If you want $option to get the _value_, instead of the number of elements in the array, you'll need to either learn about wantarray so your sub knows how it's called, or return a scalar, or do list assignment (which looks like ($option)=process_input($option). Perl is examining @data in a scalar context in your return statement, which gives the number of elements it contains, rather than its contents, because the sub was called as the rvalue of a scalar assignment.