In 5.8.0, you can open file handles to "in memory" files. To open (in read-write mode) STDERR of the current script into a scalar of the same script, do this: 
my $stderr;

close STDERR;
open STDERR, '+<', \$stderr or die $!;

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In reply to Re: Redirecting STDERR to a variable by The Mad Hatter
in thread Redirecting STDERR to a variable by Anonymous Monk

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