The first is, you can just not pass it. Filehandles are global. So you can just use it, like this:

sub foo {
   open FILE, "file.txt";
   bar();
   close FILE;
}
sub bar {
   my @lines = <FILE>;
   # do something here
}
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sub foo {
   open my $file, "file.txt";
   bar($file);
   close $file;
}
sub bar {
   my ($file) = @_;
   my @lines = <$file>;
   # do something here
}
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elusion : http://matt.diephouse.com

Lastly, I think you can use a typeglob. But I'm not sure how, and it'll be ugly.

Depends on your definition of ugly ;-)

It's not difficult either - taking up on your example:

sub foo {
  local *FILE;
  open FILE, "file.txt";
  bar(*FILE);
}
sub bar {
  my $file = shift;
  my @lines = <$file>;
  # do something here
}
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Your alternative that's using the lexical variable as a filehandle is still the best, imho, but compared to not passing it and relying on the global variable, the typeglob approach is surely better - unless the script is very short and trivially simple. Btw, note my use of local to avoid clobbering the global filehandle FILE.

-- Hofmator

thx^^

Either of your examples is potentially correct, though I suspect neigher is what you want.   my $filename = aa; will put a value into $filename if you've previously defined a suboutine "aa" that returns a value.   my $filename = <aa>; will read a line from a file that you've opened using the symbol "aa" to hold the file descriptor.

I suspect you want   my $filename = "foo"; In any case,   subroutine($filename); is the correct way to invoke a subroutine, passing whatever $filename holds as the single argument.