perl -MIO::Scalar -le 'my $s; $SH = IO::Scalar->new(\$s); print $SH "foo"; print $s'

##</code><code>##

use IO::Scalar;

my $s;
my $SH = IO::Scalar->new(\$s);

{
    local *STDOUT = $SH;
    print "foo\n";
}

print $s;

##</code><code>##

use IO::Scalar;
$string = tie *STDOUT, 'IO::Scalar';
print "foo\n"; 
print STDERR '$string: ', $string;    # Must use stderr as stdout is tied.