Another way is to do something like:

my ($x, $y, $z) = map { $_ || '' } split;
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Since undef is false in a boolean context, it will assign the empty string to variables that are undefined.

Note: This will also assign the empty string instead of zero or the string containing zero. Those also evaluate as false in a boolean context. If you just want to replace the undefined strings, do something like:

my ($x, $y, $z) = map { defined $_ ? $_ : '' } split;
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