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Encode

Section: Perl Programmers Reference Guide (3pm)
Updated: 2014-10-30
Index

NAME

Encode - character encodings

SYNOPSIS

    use Encode;

Table of Contents

Encode consists of a collection of modules whose details are too bigto fit in one document. This POD itself explains the top-level APIsand general topics at a glance. For other topics and more details,see the PODs below:

  Name                          Description  --------------------------------------------------------  Encode::Alias         Alias definitions to encodings  Encode::Encoding      Encode Implementation Base Class  Encode::Supported     List of Supported Encodings  Encode::CN            Simplified Chinese Encodings  Encode::JP            Japanese Encodings  Encode::KR            Korean Encodings  Encode::TW            Traditional Chinese Encodings  --------------------------------------------------------

DESCRIPTION

The "Encode" module provides the interfaces between Perl's stringsand the rest of the system. Perl strings are sequences ofcharacters.

The repertoire of characters that Perl can represent is at least thatdefined by the Unicode Consortium. On most platforms the ordinalvalues of the characters (as returned by "ord(ch)") is the ``Unicodecodepoint'' for the character (the exceptions are those platforms wherethe legacy encoding is some variant of EBCDIC rather than a super-setof ASCII - see perlebcdic).

Traditionally, computer data has been moved around in 8-bit chunksoften called ``bytes''. These chunks are also known as ``octets'' innetworking standards. Perl is widely used to manipulate data of manytypes - not only strings of characters representing human or computerlanguages but also ``binary'' data being the machine's representation ofnumbers, pixels in an image - or just about anything.

When Perl is processing ``binary data'', the programmer wants Perl toprocess ``sequences of bytes''. This is not a problem for Perl - as abyte has 256 possible values, it easily fits in Perl's much larger``logical character''.

TERMINOLOGY

•: character: a character in the range 0..(2**32-1) (or more).(What Perl's strings are made of.)
•: byte: a character in the range 0..255(A special case of a Perl character.)
•: octet: 8 bits of data, with ordinal values 0..255(Term for bytes passed to or from a non-Perl context, e.g. a disk file.)

PERL ENCODING API

$octets = encode(ENCODING, $string [, CHECK])

Encodes a string from Perl's internal form into ENCODING and returnsa sequence of octets. ENCODING can be either a canonical name oran alias. For encoding names and aliases, see ``Defining Aliases''.For CHECK, see ``Handling Malformed Data''.

For example, to convert a string from Perl's internal format toiso-8859-1 (also known as Latin1),

  $octets = encode("iso-8859-1", $string);

CAVEAT: When you run "$octets = encode("utf8", $string)", then $octetsmay not be equal to $string. Though they both contain the same data, the utf8 flagfor $octets is always off. When you encode anything, utf8 flag ofthe result is always off, even when it contains completely valid utf8string. See ``The UTF-8 flag'' below.

If the $string is "undef" then "undef" is returned.

$string = decode(ENCODING, $octets [, CHECK])

Decodes a sequence of octets assumed to be in ENCODING into Perl'sinternal form and returns the resulting string. As in encode(),ENCODING can be either a canonical name or an alias. For encoding namesand aliases, see ``Defining Aliases''. For CHECK, see``Handling Malformed Data''.

For example, to convert ISO-8859-1 data to a string in Perl's internal format:

  $string = decode("iso-8859-1", $octets);

CAVEAT: When you run "$string = decode("utf8", $octets)", then $stringmay not be equal to $octets. Though they both contain the same data,the utf8 flag for $string is on unless $octets entirely consists ofASCII data (or EBCDIC on EBCDIC machines). See ``The UTF-8 flag''below.

If the $string is "undef" then "undef" is returned.

[$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])

Converts in-place data between two encodings. The data in $octetsmust be encoded as octets and not as characters in Perl's internalformat. For example, to convert ISO-8859-1 data to Microsoft's CP1250encoding:

  from_to($octets, "iso-8859-1", "cp1250");

and to convert it back:

  from_to($octets, "cp1250", "iso-8859-1");

Note that because the conversion happens in place, the data to beconverted cannot be a string constant; it must be a scalar variable.

from_to() returns the length of the converted string in octets onsuccess, undef on error.

CAVEAT: The following operations look the same but are not quite so;

  from_to($data, "iso-8859-1", "utf8"); #1  $data = decode("iso-8859-1", $data);  #2

Both #1 and #2 make $data consist of a completely valid UTF-8 stringbut only #2 turns utf8 flag on. #1 is equivalent to

  $data = encode("utf8", decode("iso-8859-1", $data));

See ``The UTF-8 flag'' below.

$octets = encode_utf8($string);

Equivalent to "$octets = encode("utf8", $string);" The charactersthat comprise $string are encoded in Perl's internal format and theresult is returned as a sequence of octets. All possiblecharacters have a UTF-8 representation so this function cannot fail.

$string = decode_utf8($octets [, CHECK]);

equivalent to "$string = decode("utf8", $octets [, CHECK])".The sequence of octets represented by$octets is decoded from UTF-8 into a sequence of logicalcharacters. Not all sequences of octets form valid UTF-8 encodings, soit is possible for this call to fail. For CHECK, see``Handling Malformed Data''.

Listing available encodings

  use Encode;  @list = Encode->encodings();

Returns a list of the canonical names of the available encodings thatare loaded. To get a list of all available encodings including theones that are not loaded yet, say

  @all_encodings = Encode->encodings(":all");

Or you can give the name of a specific module.

  @with_jp = Encode->encodings("Encode::JP");

When ``::'' is not in the name, ``Encode::'' is assumed.

  @ebcdic = Encode->encodings("EBCDIC");

To find out in detail which encodings are supported by this package,see Encode::Supported.

Defining Aliases

To add a new alias to a given encoding, use:

  use Encode;  use Encode::Alias;  define_alias(newName => ENCODING);

After that, newName can be used as an alias for ENCODING.ENCODING may be either the name of an encoding or anencoding object

But before you do so, make sure the alias is nonexistent with"resolve_alias()", which returns the canonical name thereof.i.e.

  Encode::resolve_alias("latin1") eq "iso-8859-1" # true  Encode::resolve_alias("iso-8859-12")   # false; nonexistent  Encode::resolve_alias($name) eq $name  # true if $name is canonical

resolve_alias() does not need "use Encode::Alias"; it can beexported via "use Encode qw(resolve_alias)".

See Encode::Alias for details.

Encoding via PerlIO

If your perl supports PerlIO (which is the default), you can use a PerlIO layer to decodeand encode directly via a filehandle. The following two examplesare totally identical in their functionality.

  # via PerlIO  open my $in,  "<:encoding(shiftjis)", $infile  or die;  open my $out, ">:encoding(euc-jp)",   $outfile or die;  while(<$in>){ print $out $_; }

  # via from_to  open my $in,  "<", $infile  or die;  open my $out, ">", $outfile or die;  while(<$in>){    from_to($_, "shiftjis", "euc-jp", 1);    print $out $_;  }

Unfortunately, it may be that encodings are PerlIO-savvy. You can checkif your encoding is supported by PerlIO by calling the "perlio_ok"method.

  Encode::perlio_ok("hz");             # False  find_encoding("euc-cn")->perlio_ok;  # True where PerlIO is available

  use Encode qw(perlio_ok);            # exported upon request  perlio_ok("euc-jp")

Fortunately, all encodings that come with Encode core are PerlIO-savvyexcept for hz and ISO-2022-kr. For gory details, seeEncode::Encoding and Encode::PerlIO.

Handling Malformed Data

The optional CHECK argument tells Encode what to do when itencounters malformed data. Without CHECK, Encode::FB_DEFAULT ( == 0 )is assumed.

As of version 2.12 Encode supports coderef values for CHECK. See below.

NOTE: Not all encoding support this feature: Some encodings ignore CHECK argument. For example,Encode::Unicode ignores CHECK and it always croaks on error.

Now here is the list of CHECK values available

CHECK = Encode::FB_DEFAULT ( == 0)

If CHECK is 0, (en|de)code will put a substitution character inplace of a malformed character. When you encode, <subchar>will be used. When you decode the code point 0xFFFD is used. Ifthe data is supposed to be UTF-8, an optional lexical warning(category utf8) is given.

CHECK = Encode::FB_CROAK ( == 1)

If CHECK is 1, methods will die on error immediately with an errormessage. Therefore, when CHECK is set to 1, you should trap theerror with eval{} unless you really want to let it die.

CHECK = Encode::FB_QUIET

If CHECK is set to Encode::FB_QUIET, (en|de)code will immediatelyreturn the portion of the data that has been processed so far when anerror occurs. The data argument will be overwritten with everythingafter that point (that is, the unprocessed part of data). This ishandy when you have to call decode repeatedly in the case where yoursource data may contain partial multi-byte character sequences,(i.e. you are reading with a fixed-width buffer). Here is a samplecode that does exactly this:

  my $buffer = ''; my $string = '';  while(read $fh, $buffer, 256, length($buffer)){    $string .= decode($encoding, $buffer, Encode::FB_QUIET);    # $buffer now contains the unprocessed partial character  }

CHECK = Encode::FB_WARN

This is the same as above, except that it warns on error. Handy whenyou are debugging the mode above.

perlqq mode (CHECK = Encode::FB_PERLQQ)

HTML charref mode (CHECK = Encode::FB_HTMLCREF)

XML charref mode (CHECK = Encode::FB_XMLCREF)

For encodings that are implemented by Encode::XS, CHECK ==Encode::FB_PERLQQ turns (en|de)code into "perlqq" fallback mode.

When you decode, "\xHH" will be inserted for a malformed character,where HH is the hex representation of the octet that could not bedecoded to utf8. And when you encode, "\x{HHHH}" will be inserted,where HHHH is the Unicode ID of the character that cannot be foundin the character repertoire of the encoding.

HTML/XML character reference modes are about the same, in place of"\x{HHHH}", HTML uses "&#NNN;" where NNN is a decimal number andXML uses "&#xHHHH;" where HHHH is the hexadecimal number.

In Encode 2.10 or later, "LEAVE_SRC" is also implied.

The bitmask

These modes are actually set via a bitmask. Here is how the FB_XXconstants are laid out. You can import the FB_XX constants via"use Encode qw(:fallbacks)"; you can import the generic bitmaskconstants via "use Encode qw(:fallback_all)".

                     FB_DEFAULT FB_CROAK FB_QUIET FB_WARN  FB_PERLQQ DIE_ON_ERR    0x0001             X WARN_ON_ERR   0x0002                               X RETURN_ON_ERR 0x0004                      X        X LEAVE_SRC     0x0008                                        X PERLQQ        0x0100                                        X HTMLCREF      0x0200 XMLCREF       0x0400

coderef for CHECK

As of Encode 2.12 CHECK can also be a code reference which takes theord value of unmapped caharacter as an argument and returns a stringthat represents the fallback character. For instance,

  $ascii = encode("ascii", $utf8, sub{ sprintf "<U+%04X>", shift });

Acts like FB_PERLQQ but <U+XXXX> is used instead of\x{XXXX}.

Defining Encodings

To define a new encoding, use:

    use Encode qw(define_encoding);    define_encoding($object, 'canonicalName' [, alias...]);

canonicalName will be associated with $object. The objectshould provide the interface described in Encode::Encoding.If more than two arguments are provided then additionalarguments are taken as aliases for $object.

See Encode::Encoding for more details.

The UTF-8 flag

Before the introduction of utf8 support in perl, The "eq" operatorjust compared the strings represented by two scalars. Beginning withperl 5.8, "eq" compares two strings with simultaneous considerationof the utf8 flag. To explain why we made it so, I will quote page402 of "Programming Perl, 3rd ed."

Goal #1:: Old byte-oriented programs should not spontaneously break on the oldbyte-oriented data they used to work on.
Goal #2:: Old byte-oriented programs should magically start working on the newcharacter-oriented data when appropriate.
Goal #3:: Programs should run just as fast in the new character-oriented modeas in the old byte-oriented mode.
Goal #4:: Perl should remain one language, rather than forking into abyte-oriented Perl and a character-oriented Perl.

Back when "Programming Perl, 3rd ed." was written, not even Perl 5.6.0was born and many features documented in the book remainedunimplemented for a long time. Perl 5.8 corrected this and the introductionof the UTF-8 flag is one of them. You can think of this perl notion as of abyte-oriented mode (utf8 flag off) and a character-oriented mode (utf8flag on).

Here is how Encode takes care of the utf8 flag.

•

When you encode, the resulting utf8 flag is always off.

•

When you decode, the resulting utf8 flag is on unless you canunambiguously represent data. Here is the definition ofdis-ambiguity.

After "$utf8 = decode('foo', $octet);",

  When $octet is...   The utf8 flag in $utf8 is  ---------------------------------------------  In ASCII only (or EBCDIC only)            OFF  In ISO-8859-1                              ON  In any other Encoding                      ON  ---------------------------------------------

As you see, there is one exception, In ASCII. That way you can assumeGoal #1. And with Encode Goal #2 is assumed but you still have to becareful in such cases mentioned in CAVEAT paragraphs.

This utf8 flag is not visible in perl scripts, exactly for the samereason you cannot (or you don't have to) see if a scalar contains astring, integer, or floating point number. But you can still peekand poke these if you will. See the section below.

Messing with Perl's Internals

The following API uses parts of Perl's internals in the currentimplementation. As such, they are efficient but may change.

is_utf8(STRING [, CHECK]): [INTERNAL] Tests whether the UTF-8 flag is turned on in the STRING.If CHECK is true, also checks the data in STRING for being well-formedUTF-8. Returns true if successful, false otherwise.
As of perl 5.8.1, utf8 also has utf8::is_utf8().
_utf8_on(STRING): [INTERNAL] Turns on the UTF-8 flag in STRING. The data in STRING isnot checked for being well-formed UTF-8. Do not use unless youknow that the STRING is well-formed UTF-8. Returns the previousstate of the UTF-8 flag (so please don't treat the return value asindicating success or failure), or "undef" if STRING is not a string.
_utf8_off(STRING): [INTERNAL] Turns off the UTF-8 flag in STRING. Do not use frivolously.Returns the previous state of the UTF-8 flag (so please don't treat thereturn value as indicating success or failure), or "undef" if STRING isnot a string.

UTF-8 vs. utf8

  ....We now view strings not as sequences of bytes, but as sequences  of numbers in the range 0 .. 2**32-1 (or in the case of 64-bit  computers, 0 .. 2**64-1) -- Programming Perl, 3rd ed.

That has been the perl's notion of UTF-8 but official UTF-8 is morestrict; Its ranges is much narrower (0 .. 10FFFF), some sequences arenot allowed (i.e. Those used in the surrogate pair, 0xFFFE, et al).

Now that is overruled by Larry Wall himself.

  From: Larry Wall <larryAATTwall.org>  Date: December 04, 2004 11:51:58 JST  To: perl-unicodeAATTperl.org  Subject: Re: Make Encode.pm support the real UTF-8  Message-Id: <20041204025158.GA28754AATTwall.org>

  On Fri, Dec 03, 2004 at 10:12:12PM +0000, Tim Bunce wrote:  : I've no problem with 'utf8' being perl's unrestricted uft8 encoding,  : but "UTF-8" is the name of the standard and should give the  : corresponding behaviour.

  For what it's worth, that's how I've always kept them straight in my  head.

  Also for what it's worth, Perl 6 will mostly default to strict but  make it easy to switch back to lax.

  Larry

Do you copy? As of Perl 5.8.7, UTF-8 means strict, official UTF-8while utf8 means liberal, lax, version thereof. And Encode version2.10 or later thus groks the difference between "UTF-8" and C``utf8''.

  encode("utf8",  "\x{FFFF_FFFF}", 1); # okay  encode("UTF-8", "\x{FFFF_FFFF}", 1); # croaks

"UTF-8" in Encode is actually a canonical name for "utf-8-strict".Yes, the hyphen between ``UTF'' and ``8'' is important. Without it Encodegoes ``liberal''

  find_encoding("UTF-8")->name # is 'utf-8-strict'  find_encoding("utf-8")->name # ditto. names are case insensitive  find_encoding("utf8")->name  # ditto. "_" are treated as "-"  find_encoding("UTF8")->name  # is 'utf8'.

MAINTAINER

This project was originated by Nick Ing-Simmons and later maintainedby Dan Kogai <dankogaiAATTdan.co.jp>. See AUTHORS for a fulllist of people involved. For any questions, use<perl-unicodeAATTperl.org> so we can all share.

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