That is a warning, not an error. join will be happy to join undef, @foo; to the same effect as joining with an empty string.

You can turn the warning off in modern perl with { no warnings 'uninitialized'; ... } That is lexically scoped, which is why I used a bare block there. Older perl is more awkward about switching off warnings. It is not selective and there are peculiar rules to follow. See the docs for them.

(Added) Looking harder at your code, I suspect that some of your data is not providing array elements that you explicitly index. If so, perhaps you need to check your data parsing.

After Compline,
Zaxo