$log = "something", do_split($log) should have a string, right?

Right, but that string is in $_[0] not $_.
Try putting: 

shift;

[download]
as the first line of your sub. That will pop $_[0] into $_;

In reply to RE:(3) strange uninitialized value problem by swiftone
in thread strange uninitialized value problem by jjhorner

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