Notice how STDIN redirection doesn't work below.

>copy con script.pl
while (<STDIN>) { s/[aeiou]/!/ig; print; }
^Z
>script.pl < script.pl
>perl script.pl < script.pl
wh!l! (<STD!N>) { s/[!!!!!]/!/!g; pr!nt; }
>ver
Microsoft Windows XP [Version 5.1.2600]
[download]

It works fine with batch files, however. That's where pl2bat comes in. It makes it so you don't have to explicitly mention "perl" to execute the script, without suffering from the above bug.