You're trying to use talk about the filehandle symbolically, that is, construct its name: 

my $fh = "OUTPUT" . $i;

[download]

Don't do that. Since version 5.6, Perl allows you to conveniently put filhandles in lexically scoped variables. In your case you're indexing by a number, so an array of handles is probably the best choice. 

# before the if ($. == 1)
my @fhs;

...

# open one
open $fhs[$i], ">", $filename or die "Cannot open the output file: $!"
+;

...

# use it
print {$fhs[$i]} "$line[0]\t$line[$i]\n";

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Note it's important to control the scope of @fhs, so it's visible to your code that uses it. When it goes out of scope, the files are closed.

Update: fixed syntax error, thanks eyespoplikeamosquito++!

In reply to Re: Multiple simultaneous filehandles by gaal
in thread Multiple simultaneous filehandles by ezekiel

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