my @field = m{ \A (.{20}) \s (.{20}) \s (.{3}) \s (.{3}) \z }msx

##</code><code>##

my @field = unpack "A20 x A20 x A3 x A3", $_;

##</code><code>##

my @field = m{ \A (.{1,20}?) \s+ (.{1,20}?) \s+ (.{1,3}?) \s+ (.{1,3}?) \z }msx