to call functions B<outside> your Perl code, such as POSIX::system,
in which case they are able to run arbitrary external code.
+=item *
+
+Hash keys are B<never> tainted.
+
=back
For efficiency reasons, Perl takes a conservative view of
Because taintedness is associated with each scalar value, some
elements of an array or hash can be tainted and others not.
-The keys of a hash are never tainted.
+The keys of a hash are B<never> tainted.
For example:
will automagically remove any duplicated directories, while the later
will not.
+Note that if a tainted string is added to C<@INC>, the following
+problem will be reported:
+
+ Insecure dependency in require while running with -T switch
+
=head2 Cleaning Up Your Path
-For "Insecure C<$ENV{PATH}>" messages, you need to set C<$ENV{'PATH'}> to a
-known value, and each directory in the path must be non-writable by others
-than its owner and group. You may be surprised to get this message even
-if the pathname to your executable is fully qualified. This is I<not>
-generated because you didn't supply a full path to the program; instead,
-it's generated because you never set your PATH environment variable, or
-you didn't set it to something that was safe. Because Perl can't
-guarantee that the executable in question isn't itself going to turn
-around and execute some other program that is dependent on your PATH, it
-makes sure you set the PATH.
+For "Insecure C<$ENV{PATH}>" messages, you need to set C<$ENV{'PATH'}> to
+a known value, and each directory in the path must be absolute and
+non-writable by others than its owner and group. You may be surprised to
+get this message even if the pathname to your executable is fully
+qualified. This is I<not> generated because you didn't supply a full path
+to the program; instead, it's generated because you never set your PATH
+environment variable, or you didn't set it to something that was safe.
+Because Perl can't guarantee that the executable in question isn't itself
+going to turn around and execute some other program that is dependent on
+your PATH, it makes sure you set the PATH.
The PATH isn't the only environment variable which can cause problems.
Because some shells may use the variables IFS, CDPATH, ENV, and
=item *
-Regular expressions - Perl's regular expression engine is so called
-NFA (Non-Finite Automaton), which among other things means that it can
-rather easily consume large amounts of both time and space if the
+Regular expressions - Perl's regular expression engine is so called NFA
+(Non-deterministic Finite Automaton), which among other things means that
+it can rather easily consume large amounts of both time and space if the
regular expression may match in several ways. Careful crafting of the
regular expressions can help but quite often there really isn't much
one can do (the book "Mastering Regular Expressions" is required
=back
See L<http://www.cs.rice.edu/~scrosby/hash/> for more information,
-and any computer science text book on the algorithmic complexity.
+and any computer science textbook on the algorithmic complexity.
=head1 SEE ALSO