with str_three and str_four the resulting array is empty (or may I say "undefined")
No, you may not.

Once you execute my @array =  split ( "," , $_ );, @array has a defined value, period. A variable with an undefined (or uninitialized, for that matter) value is a variable which has either never had a value assigned to it or has had its value explicitly removed. Your split assigns a value to @array, therefore @array is not undefined. (If split could return undef, then @array could potentially end up undefined, but split doesn't do that. Even split ",", undef; returns an empty list, which is a defined value.)

If you want to preserve the empty (not undefined!) values in your input strings, give split a -1 (or any negative integer) as an additional parameter to tell it to keep all values, including leading/trailing empty values: 

$ perl -w -E '@values = split ",", "1,2,3,4", -1; say join ",", @value
+s'
1,2,3,4
$ perl -w -E '@values = split ",", ",,3,", -1; say join ",", @values'
,,3,
$ perl -w -E '@values = split ",", ",,,", -1; say join ",", @values'
,,,

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In reply to Re: How to differentiate an empty array from an unitialized one? by dsheroh
in thread How to differentiate an empty array from an unitialized one? by iatros

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