If I got your specs correctly, and your data is separated by spaces, you can split the line and use a hash to store the opened filehandles. This code should work:

Update: Updated split - Thanks Skeeve.

open my $fh_input, "<", "input.txt" or die "$!";
my %fh = ();
while (<$fh_input>) {
    chomp;
    my ($filename, $content) = split /\s+/, $_, 2;
    my $fh = undef;
    $fh = $fh{$filename} if defined $fh{$filename};
    if (not defined $fh{$filename}) {
        open $fh, ">", "$filename.out" or die "$!";
        $fh{$filename} = $fh;
    }
    else {
        $fh = $fh{$filename};
    }
    print $fh $content, "\n";
}

foreach (keys %fh) {
   close $fh{$_};
}
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