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my @field = m{ \A (.{20}) \s (.{20}) \s (.{3}) \s (.{3}) \z }msx
my @field = unpack "A20 x A20 x A3 x A3", $_;
my @field = m{ \A (.{1,20}?) \s+ (.{1,20}?) \s+ (.{1,3}?) \s+ (.{1,3}? +) \z }msx