Why are you openning and closing the same files over and over? This is expensive and error-prone. Just do something like this: 
my @files = ("1.txt", "2.txt", "3.txt");
my @fhs;

foreach my $file (@files) {
     open($fh, $file) || die;
     push(@fhs, $fh);
}
open(MIXED, "mixed.txt") || die;
while (1) {
     foreach $fh (@fhs) {
         $line = <$fh>;
         last if (eof($fh));
         print MIXED $line;
     }
}
map { close($_); } @fhs;
close(MIXED);

[download]
Note that this code assumes all your files have the same number of lines. If this is not the case, you have to do some extra trickery to not break out of the loop until all files are empty...

In reply to Re: combine multiple files into one (line by line) by ton
in thread combine multiple files into one (line by line) by Anonymous Monk

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