Thanks a lot, GrandFather. Now I get the following errors while it does not print out anything to the file. "my" variable $in masks earlier declaration in same scope (line 19) use of uninitialized value $key in hash element (line26) use of uninitialized value $key in printf (line26) 
#!/usr/bin/perl
use strict;
use warnings;

my $data1 = "/DATA/input.txt";
my $data2 = "/DATA/input2.txt";
my $data3 = "/DATA/output.txt";

my %data;
my @columnNames;
my $key;

[line 19]open my $in, '<', $data1 or die "Unable to open $data1: $!";
push @columnNames, parseFile (\%data, $in);
close $in;

open my $in, '<', $data2 or die "Unable to open $data2: $!";
push @columnNames, parseFile (\%data, $in);
close $in;

my $format = (('%-9s ') x (@columnNames + 1)) . "\n";

open my $out, '>', $data3 or die "Unable to open $data3: $!";
(line26)printf $out $format, $key, @{$data{$key}}{@columnNames};


for my $key (sort keys %data) {
    next if keys %{$data{$key}} != @columnNames;
    
    printf $format, $key, @{$data{$key}}{@columnNames};
}

sub parseFile {
    my ($dataRef, $inFile) = @_;
    my $header = <$inFile>;
    my ($keyColumn, @columns) = map {chomp; split} $header;

    while (defined (my $line = <$inFile>)) {
            chomp $line;
    
        my ($key, @data) = split /\s+/, $line;
        @{$dataRef->{$key}}{@columns} = @data;
    }
    
    return @columns;
}

[download]
It prints out the output on dos-screen, though. (but not into file)

In reply to Re^5: Hash w/ multiple values + merging by sophix
in thread Hash w/ multiple values + merging by sophix

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