Sidac:

You can tell perl to read entire records at a time by setting the input record separator to a blank line (see perlvar). Then you can split the record on whitespace, like so:

$ cat t.pl
#!/usr/bin/perl
use strict;
use warnings;
use List::MoreUtils qw<pairwise>;

$/="";
my @list1 = split /\s+/, <DATA>;
my @list2 = split /\s+/, <DATA>;
my @diff = pairwise { $b-$a } @list2, @list1;

print join(", ", @diff),"\n";
__DATA__
42.034 41.630 40.158 26.823
26.366 25.289 23.949

34.712 35.133 35.185 35.577
28.463 28.412 30.831

$ perl t.pl
Name "main::b" used only once: possible typo at t.pl line 9.
Name "main::a" used only once: possible typo at t.pl line 9.
7.322, 6.497, 4.973, -8.754, -2.097, -3.123, -6.882
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...roboticus

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