$ perl -Mre=debug barney
Compiling REx "^barney"
Final program:
   1: MBOL (2)
   2: EXACT <barney> (5)
   5: END (0)
anchored "barney" at 0 (checking anchored) anchored(MBOL) minlen 6
Guessing start of match in sv for REx "^barney" against "This is a wilma line%n         barney is on this line%n     "..
.
Found anchored substr "barney" at offset 30...
Found /^/m, restarting lookup for check-string at offset 53...
Did not find anchored substr "barney"...
Match rejected by optimizer
Barney not found
Freeing REx: "^barney"