dispatchers are good, but with DRY principle you may use code like this

use warnings;
use strict;

sub unpack_a { print "a(@_)\n"; 11 }
sub unpack_b { print "b(@_)\n"; 22 }

my $RECORD_SEQ_ID = 'a';
local $_ = 0;
my @lines = 42;

my $res = do { no strict 'refs'; &{"unpack_$RECORD_SEQ_ID"} ($lines[$_
+]) };

print $res;
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Yes, it's not so secure if you don't understand what you're doing, and it's around 20% slower then dispatchers which is usually does not matter.