There are all kinds of interesting games you can play with pack, and it should be easy to encapsulate your solution in a function (with lotsa validation) so that maintainers only see data. See below.

Note that the  @ pack template specifier fills with nulls, so if you want space-filling, you need the
    $packed =~ tr{\000}{ };
statement. Note also that  @ is absolute, so maybe play around and see, e.g., what happens if the  date offset is set to 1 or 2. 

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"use constant ORDER => qw(date  client_id  info);
 ;;
 my %o_l = (
   date      => { qw(off  0  len 6  field 040814)             },
   client_id => { qw(off  6  len 8  field WayTooMuchClientID) },
   info      => { qw(off 20  len 7  field G1APD)              },
   );
 ;;
 my $fields =
   join '  ',
   map  qq{\@$o_l{$_}{off} A$o_l{$_}{len}},
   map  { exists $o_l{$_} or die qq{bad '$_'};  $_; }
   ORDER
   ;
 ;;
 my $packed = pack $fields, map $o_l{$_}{field}, ORDER;
 $packed =~ tr{\000}{ };
 print 'packed len ', length $packed, qq{ '$packed'};
 ;;
 my $total = 30;
 die 'truncation!' if length($packed) > $total;
 my $line = pack qq{A$total}, $packed;
 print 'total  len ', length($line), qq{ '$line'};
 ;;
 dd \$line;
"
packed len 27 '040814WayTooMu      G1APD  '
total  len 30 '040814WayTooMu      G1APD     '
\"040814WayTooMu      G1APD     "

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In reply to Re^3: Google has failed me! Using pack and substr for fixed width file output by AnomalousMonk
in thread Google has failed me! Using pack and substr for fixed width file output by spudulike

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