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readFile( 'Text1', \@array1, \@data1 );
readFile( 'Text1', \@array2, \@data2 );
...
   close $fh;
   return;
}

use Data::Dump qw/ dd /;
## this?
...
    dd( \%RedText, \%DerText );
}

"entry_id", "fist_number", "second_letter"
$hash{"entry_id"}{"fist_number"} = "second_letter";
$bothfiles{first_file}{"entry_id"}{"fist_number"} = "second_letter";