If you suspect that a regex isn't parsed the way you wanted it, you can use re 'debug'; to find out: 
$ perl -Mre=debug -wle 'm/C$\n^D/'
Freeing REx: `","'
Omitting $` $& $' support.

EXECUTING...

Compiling REx `C
n^D'
size 6 Got 52 bytes for offset annotations.
first at 1
rarest char D at 3
   1: EXACT <C\nn>(3)
   3: BOL(4)
   4: EXACT <D>(6)
   6: END(0)
anchored "C
...

[download]
You don't have to understand everything to notice that the EXACT <C\nn> isn't what you were after. The literal <c>n has to come from the ...\n in the regex, so the thing before it (a newline) has to come from the previous token in the regex.

In reply to Re^2: Why \n matches but not $^? (weight) by moritz
in thread Why \n matches but not $^? by tel2

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