decryption filter in C and statically link the decryption module into
the Perl binary. For further tips to make life difficult for the
potential cracker, see the file I<decrypt.pm> in the source filters
-module.
+distribution.
=back
task: C<Filter::exec> and C<Filter::sh>. Both allow you to run any
external executable. Both use a coprocess to control the flow of data
into and out of the external executable. (For details on coprocesses,
-see Stephens, W.R. "Advanced Programming in the UNIX Environment."
+see Stephens, W.R., "Advanced Programming in the UNIX Environment."
Addison-Wesley, ISBN 0-210-56317-7, pages 441-445.) The difference
between them is that C<Filter::exec> spawns the external command
directly, while C<Filter::sh> spawns a shell to execute the external
}
## DEBUG_END
-When the C<DEBUG> environment variable exists, the filter ensures that
-Perl parses only the code between the C<DEBUG_BEGIN> and C<DEBUG_END>
-markers. That means that when C<DEBUG> does exist, the code above
+The filter ensures that Perl parses the code between the <DEBUG_BEGIN>
+and C<DEBUG_END> markers only when the C<DEBUG> environment variable
+exists. That means that when C<DEBUG> does exist, the code above
should be passed through the filter unchanged. The marker lines can
also be passed through as-is, because the Perl parser will see them as
comment lines. When C<DEBUG> isn't set, we need a way to disable the