Some code: (you may have to refine a bit, do things like output formating, sorting etc.)

use Data::Dumper;

use strict;
use warnings;

my $hash;

open(FILE, "<", "file1.txt");
while (<FILE>) {
    my ($k, $v) = split " ";
    $hash->{$k}->[0] = $v;
}
close FILE;

open(FILE, "<", "file2.txt");
while (<FILE>) { 
    my ($v, $k) = split " ";
    $k = /(complex\.\d+)/;
    $hash->{$1}->[1] = $v;
}
close FILE;

print Dumper($hash);

open (OUT, ">", "out.txt");
for my $key (keys(%$hash)) {
    print OUT $key . " " . $hash->{$key}->[0] . " " . $hash->{$key}->[
+1] . "\n";
}
close OUT;
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