$ perl -MScalar::Util=weaken -e'weaken(\my $var)'
Weak references are not implemented in the version of perl at -e line 0
BEGIN failed--compilation aborted.

##</code><code>##

$ locate Util.so
/usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/auto/List/Util/Util.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/APR/Util/Util.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/Apache2/ConnectionUtil/ConnectionUtil.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/Apache2/RequestUtil/RequestUtil.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/Apache2/ServerUtil/ServerUtil.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/Apache2/Util/Util.so
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/ModPerl/Util/Util.so

##</code><code>##


$ perl -e 'print join( "\n", @INC), "\n";'
/usr/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.8
/usr/lib/perl5/site_perl
/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.8
/usr/lib/perl5/vendor_perl
/usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi
/usr/lib/perl5/5.8.8
.