IMO, the most convenient way to handle fixed-width records is with pack to write and unpack to read. Pack is usable either with arrays or lists of variables.

my @data = qr/foo bar bazaquuxinator/;
my $format = q(A3 A10 A3 A35);
my $line = pack $format, @data;
print $line, $/;
my $line = pack $format, @data[0,1], 'quux', $data[2];
print $line, $/;
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That prints,

foobar       baz                                   
foobar       quubazaquuxinator                     
$

Unpacking with the same format string splits run-together items at the correct places. Notice that too-long data is truncated to the field width. The first printed line was constructed with not enough data for the format, so pack put 35 blanks at the end.