1. Ike's code assumes a one-to-one correspondence between the two record types.

   Well founded based on the OPs sample, but these type of mainframe 'carded' records often have multiple secondary records to each primary record.

2. If the OP confirmed that they were one-to-one, then you could also do a single read for both record types and pre-partition also.
3. The problem with unpack is that the template must be re-parsed for every record.

   And recent fairly extensive additions to the format specifications have taken some toll on performance.

   With these short, simply structured records that doesn't exact too much of a penalty, but with longer, more complex records it can.

4. The idea of pre-partitioning the input buffer with an array of substr refs is that simply assigning each record into the pre-partitioned buffer effectively does the parsing and splitting.

   I think the technique is worth a mention for its own sake.

A quick run of the two posted programs over the same file shows mine to be a tad quicker, but insignificantly. If I adjust mine to the same assumptions as Ike's, (or Ike's to the same assumptions as mine), then mine comes in ~20% quicker. Only a couple of seconds on 1e6 lines, but could be worth having for 100e6.

c:\test>901649-buk 901649.dat >nul
Took 9.283 for 1000000 lines

c:\test>901649-ike 901649.dat >nul
Took 11.305 for 1000000 lines
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Code tested:

#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my $start = time;

my $rec = chr(0) x 123;

my @type3l = split ':', '02:10:33:15:19:10:3:18:6:4';
my $n = 0;
my @type3o = map{
    $n += $_; $n - $_;
} @type3l;

my @type3 = map \substr( $rec, $type3o[ $_ ], $type3l[ $_ ] ), 0 .. $#
+type3o;

my @typeOl = split ':', '02:98:11:9';
$n = 0;
my @typeOo = map{
    $n += $_; $n - $_;
} @typeOl;

my @typeO = map \substr( $rec, $typeOo[ $_ ], $typeOl[ $_ ] ), 0 .. $#
+typeOo;

$/ = \123;
until( eof() ) {
    substr( $rec, 0 ) = <>;
    if( $rec =~ /^03/ ) {
        print join '/', map $$_, @type3;
    }
    else {
        print join '|', map $$_, @typeO;
    }
}

printf STDERR "Took %.3f for $. lines\n", time() - $start;
[download]

#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my $start = time;

$/ = \123;
while( <> ) {
    if( /^03/ ) {
        my @fields = unpack "A2 A10 A33 A15 A19 A10 A3 A18 A6 A4 x3", 
+$_;
        print join '/', @fields;
    }
    else {
        my @fields = unpack "A2 A98 A11 A9 x3", $_;
        print join '|', @fields;
    }
}

printf STDERR "Took %.3f for $. lines\n", time() - $start;
[download]