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Re^2: Default encoding rules leave me puzzled... (use open qw/ :std :locale /;

by kzwix (Novice)
on Jun 20, 2014 at 09:36 UTC ( #1090597=note: print w/ replies, xml ) Need Help??


in reply to Re: Default encoding rules leave me puzzled... (use open qw/ :std :locale /;
in thread Default encoding rules leave me puzzled...

Sorry, I realize I wasn't specific enough:
I've read about Encode, and successfully used it in a previous project. I know about the need to decode and encode streams, too. However, it seemed to me that Perl did some of this job itself (as I had tried to explicitly decode data from the standard input, or from command-line arguments, and had experienced strange results)

So, is there some place where it is explicitly stated what is converted by perl, in a transparent manner, and what isn't ?

Furthermore, even though I didn't Encode or Decode the streams, shouldn't it "just work", if the scalar value is specified in UTF-8 (because the file is encoded as such), and Perl is AWARE that it is UTF-8 (because of 'use utf8;'), and Perl stores it internally in UTF-8, and the expected output format is UTF-8 too ?

I'm pretty sure there is a catch I haven't figured out, there, but pointing it to me, even if obvious, could help. Thanks !

EDIT: I've run a short test, using a Latin-1 terminal (this test script is fully encoded in UTF-8):

#!/usr/bin/perl use utf8; use Encode; $\ = "\n"; my $unicodeScalar = "Je suis une chaîne accentuée là où il faut."; print '['.Encode::is_utf8($unicodeScalar).'] '.$unicodeScalar;

Using my Latin-1 terminal, I displayed the source file, and, sure enough, the contents were garbled (2 strange bytes for each accentuated character, which confirmed me the file was truly UTF-8), then I ran the script. And I got a perfect display.

So, does Perl assume by default, even in a UTF-8 environment, that it should output everything in Latin-1 ?


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Re^3: Default encoding rules leave me puzzled... (use open qw/ :std :locale /;
by moritz (Cardinal) on Jun 20, 2014 at 12:26 UTC
    So, does Perl assume by default, even in a UTF-8 environment, that it should output everything in Latin-1 ?

    Perl tries to not convert anything at all, automatically.

    And since Latin-1 (mostly?) maps the first 256 codepoints 1:1 to bytes, outputting something without any conversion is the same as outputting it as Latin-1.

    Note that this round-trips binary data, which means that if your scripts or input use UTF-8, and you don't use utf8;, the output will be UTF-8 again.

    But, Latin-1 is limited to codepoints up to 255, so if something higher than that shows up in your string, perl falls back to UTF-8 (and warns).

    (As always, I'm linking to Encodings and Unicode in Perl, in the hope that it's useful to you).

      I'm sorry, but I think that your "Perl tries to not convert anything at all, automatically" statement is wrong.
      I mean, else, why would a string internally stored as UTF-8 be converted to Latin-1 when sent to the standard output ?
      (That is, without having used any funny encoding/decoding/layer stuff...)

        It's your use utf8; statement that explicitly converts the source code to perl's internal format, which happens to be latin-1 in this case. The output operation then doesn't convert anything. Maybe I should have said that no implicit conversion takes place, because I don't coutn the use utf8; as automatic/implicit.

        I mean, else, why would a string internally stored as UTF-8 be converted to Latin-1 when sent to the standard output ?

        Because you are printing the string, not its internal representation. The layout of a scalar is irrelevant.

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