Using unix, the comm utility already does this (options: -1 suppress lines unique to file 1 and -3 suppress common lines, leaving only column 2 as output: the lines unique to file 2).
comm -13 file1 file2 > file3

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To address the OP Perl, use regexp matching to isolate the first column - which is the correct key for the hash. It also means you then don't need to chop or chomp everything only to have to put the \n back. Also @names doesn't function as an array coercion of %names but as a completely separate piece of storage.

The following is now updated to sort the output.

open FIRST,"file1" or die "$!: file1\n";
open LAST,"file2" or die "$!: file2\n";
open NEW,">file3" or die "$!: file3\n";
my %names = ();
my %n2 = ();
while (<FIRST>) {
   /^(\S+)/;
   $names{$1} = 1;
}
close FIRST;
while (<LAST>) {
   /^(\S+)/;
   $names{$1} or $n2{$1} = $_;
}
close LAST;
print NEW $n2{ $col1 } for my $col1 ( sort keys %n2 );
close NEW;

[download]

-M

Free your mind

In reply to Re: file compare and populate by Moron
in thread file compare and populate by Anonymous Monk

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