perl -D512 -e '$_ = "f\n";/.*\z/s'
Compiling REx `.*\z'
size 4 Got 36 bytes for offset annotations.
first at 2
rarest char 
 at 0
   1: STAR(3)
   2:   SANY(0)
   3: EOS(4)
   4: END(0)
floating ""$ at 0..2147483647 (checking floating) anchored(SBOL) implicit minlen 0 
Offsets: [4]
        2[1] 1[1] 3[2] 5[0] 
Omitting $` $& $' support.

EXECUTING...

Guessing start of match, REx ".*\z" against "f
"...
Found floating substr ""$ at offset 1...
Guessed: match at offset 0
Matching REx ".*\z" against "f
"
  Setting an EVAL scope, savestack=6
   0 <> <f
>              |  1:  STAR
                           SANY can match 2 times out of 2147483647...
  Setting an EVAL scope, savestack=6
   2 <f
> <>              |  3:    EOS
   2 <f
> <>              |  4:    END
Match successful!
Freeing REx: `".*\\z"'