comment on

Because in a //m, the end of string matching "f\n" is set before the '\n' if the '\n' is trailing. The '\n' is skipped in the match, but the position after "f" isn't the end of the string:

perl -D512 -e '$_ = "f\n";/.*\z/'
Compiling REx `.*\z'
size 4 Got 36 bytes for offset annotations.
first at 2
rarest char 
 at 0
   1: STAR(3)
   2:   REG_ANY(0)
   3: EOS(4)
   4: END(0)
floating ""$ at 0..2147483647 (checking floating) anchored(MBOL) impli
+cit 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...
Position at offset 0 does not contradict /^/m...
Guessed: match at offset 0
Matching REx ".*\z" against "f
"
  Setting an EVAL scope, savestack=3
   0 <> <f
>              |  1:  STAR
                           REG_ANY can match 1 times out of 2147483647
+...
  Setting an EVAL scope, savestack=3
   1 <f> <
>              |  3:    EOS
                              failed...
                            failed...
Guessing start of match, REx ".*\z" against "
"...
Found floating substr ""$ at offset 0...
Position at offset 0 does not contradict /^/m...
Guessed: match at offset 0
  Setting an EVAL scope, savestack=3
   1 <f> <
>              |  1:  STAR
                           REG_ANY can match 0 times out of 2147483647
+...
  Setting an EVAL scope, savestack=3
   1 <f> <
>              |  3:    EOS
                              failed...
                            failed...
Match failed
Freeing REx: `".*\\z"'
[download]

The matching isn't extended after the "\n". Whereas here

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) impli
+cit 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"'
[download]

you can see that the '\z' (<> in the debug output) is found after the "\n":

  Setting an EVAL scope, savestack=6
   2 <f
> <>              |  3:    EOS
   2 <f
> <>              |  4:    END
[download]

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

In reply to Re^3: Strange regex to test for newlines: /.*\z/ by shmem
in thread Strange regex to test for newlines: /.*\z/ by betterworld

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