If your using 5.8.x, then you can use the "in-memory file" form of open.

#! perl -slw
use strict;

sub IO2Mem{
    my( $memRef, $mode, $io ) = @_;
    die 'Usage: IO2Mem( scalarRef [, mode] )' 
        unless ref $memRef eq 'SCALAR';
    open $io, $mode || '>', $memRef or die $!;
    return select $io;
}

my $memory;
my $saved = IO2Mem( \$memory );

print 'Hello world!' for 1 .. 10;
$memory =~ s[o w][o, W]g;

select $saved;
print $memory;

__END__
P:\test>test2
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
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