As already mentioned, on Perl 5.6+ you can simply

open my $fh, "<", $filename;
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and then pass $fh around. If you want to be compatible with earlier versions, it is only slightly more verbose:

use Symbol qw(gensym);

# ...

open +(my $fh = gensym), "<$filename";
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And yes, this is definitely going to stay with us in Perl 5. In Perl 6 you'll be doing things entirely differently:

my $fh = open "<", $filename;
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Though the other syntax will probably remain supported. Still I'm definitely switching to this new construct as soon as possible.

Makeshifts last the longest.