That's a bit like one of my Japhs:

BEGIN{$SIG{__WARN__}=sub{$_=pop;y-_- -;print/".*(.)"/;
truncate$0,-1+-s$0;exec$0;}}//rekcaH_lreP_rehtona_tsuJ
[download]

Or:

BEGIN{$|=$SIG{__WARN__}=sub{$_=$_[0];y-_- -;print/(.)"$/;seek _,-open(
+_
,"+<$0"),2;truncate _,tell _;close _;exec$0}}//rekcaH_lreP_rehtona_tsu
+J
[download]

(for both, make sure there are no trailing newlines).

Note that in my versions the actual source code (that is, the characters in the file) is corrected. Run it once, and you see the familiar line - run it a second time, and nothing happens: the code has been corrected!

Abigail