Convert a program to a palindromic program
Perl, 55 54 bytes



undef$/;$a=&lt;&gt;."\n__END__\n";print$a,scalar reverse$a;


Reads program source from stdin and writes to stdout.

Result of running on itself:

undef$/;$a=&lt;&gt;."\n__END__\n";print$a,scalar reverse$a;

__END__

__DNE__

;a$esrever ralacs,a$tnirp;"n\__DNE__n\".&gt;&lt;=a$;/$fednu