For completeness–

perl -Mutf8 -CSD -E 'say length "Kü"'
# 2
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Yes but only if it's a character-string, i.e. the utf8 flag is set.

But the OP said the flag is not set.

edit

not sure what -CSD means.

update

got it perlrun

The -C flag controls some of the Perl Unicode features.


As of 5.8.1, the -C can be followed either by a number or a list of option letters. The letters, their numeric values, and effects are as follows; listing the letters is equal to summing the numbers.


        I     1   STDIN is assumed to be in UTF-8
        O     2   STDOUT will be in UTF-8
        E     4   STDERR will be in UTF-8
        S     7   I + O + E
        i     8   UTF-8 is the default PerlIO layer for input streams
        o    16   UTF-8 is the default PerlIO layer for output streams
        D    24   i + o

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

Quite right. Those are the default I/O UTF-8 flags. tchrist included some of them in his recommendations on that monster SO post. Included just as an example of what’s correct. If the length is giving bytes instead of length. It’s broken already and that step, or one before it, is the problem. If the OP included an SSCCE, I’d be more helpful. Possibly… :P

Which is more helpful for us than the OP's copy and paste.

> A decent print unpack 'H*',$data does the same with less fuss.

True, but unpack tells me "why" it went wrong? ;)

Update

> but displays as 'Kü',

Provided code areas in the monastery are encoded in utf8. I vividly remember problems here. *

*) the monastery is using windows-1252

°)

--- Testing: Täst:  "T\xE4st"
SV = PVMG(0x29c3c98) at 0x29c1fa8
  REFCNT = 1
  FLAGS = (SMG,POK,pIOK,pNOK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x24c9c68 "T\303\244st"\0 [UTF8 "T\x{e4}st"]
  CUR = 5
  LEN = 10
  MAGIC = 0x2ab1b38
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 4

> A decent print unpack 'H*',$data does the same with less fuss.

Actually, why should I bother to spot the non-ASCII between all the hex-codes? °

Please compare

 
 DB<50> $data = 'Künzler'

  DB<51> print unpack 'H*',$data
4b816e7a6c6572                             # ORLY?
  DB<52> use Data::Dump qw/pp dd/

  DB<53> dd $data
"K\x81nzler"                               # <---

  DB<54> use Devel::Peek

  DB<55> Dump $data
SV = PVNV(0xd9adb8) at 0x351ac30
  REFCNT = 1
  FLAGS = (POK,IsCOW,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x355bcd8 "K\201nzler"\0            # <---
  CUR = 7
  LEN = 10
  COW_REFCNT = 2

  DB<56>
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Hint: this time not UTF8, did you notice easily?

Devel::Peek is core and shows multiple relevant infos in one command.

It has some minor disadvantages, but if the OP had shown us the output we'd knew immediately that his code is correct, except the debugger settings.

Telling people explicitly not to use it is pretty surprising ...

°) yes I know that ASCII is below 0x80 and how to spot utf8 multi-bytes. But do others?

And normally I use a water heater when I need tea and don't start to collect decent wood in the forest. ;-)