Table of Contents¶

Encode consists of a collection of modules whose details are too extensive to fit in one document. This one itself explains the top-level APIs and general topics at a glance. For other topics and more details, see the documentation for these modules:

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

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, such as a disk file, standard I/O stream, database, command-line argument, environment variable, socket etc.

Basic methods¶

encode

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

Encodes the scalar value STRING from Perl's internal form into ENCODING and returns a sequence of octets. ENCODING can be either a canonical name or an 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 into ISO-8859-1, also known as Latin1:

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

CAVEAT: When you run "$octets = encode("utf8", $string)", then $octets might not be equal to $string. Though both contain the same data, the UTF8 flag for $octets is always off. When you encode anything, the UTF8 flag on the result is always off, even when it contains a completely valid utf8 string. See "The UTF8 flag" below.

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

decode

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

This function returns the string that results from decoding the scalar value OCTETS, assumed to be a sequence of octets in ENCODING, into Perl's internal form. The returns the resulting string. As with encode(), ENCODING can be either a canonical name or an alias. For encoding names and aliases, see "Defining Aliases"; for CHECK, see "Handling Malformed Data".

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

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

CAVEAT: When you run "$string = decode("utf8", $octets)", then $string might not be equal to $octets. Though both contain the same data, the UTF8 flag for $string is on unless $octets consists entirely of ASCII data on ASCII machines or EBCDIC on EBCDIC machines. See "The UTF8 flag" below.

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

find_encoding

  [$obj =] find_encoding(ENCODING)

Returns the encoding object corresponding to ENCODING. Returns "undef" if no matching ENCODING is find. The returned object is what does the actual encoding or decoding.

  $utf8 = decode($name, $bytes);

is in fact

    $utf8 = do {
        $obj = find_encoding($name);
        croak qq(encoding "$name" not found) unless ref $obj;
        $obj->decode($bytes);
    };

with more error checking.

You can therefore save time by reusing this object as follows;

    my $enc = find_encoding("iso-8859-1");
    while(<>) {
        my $utf8 = $enc->decode($_);
        ... # now do something with $utf8;
    }

Besides "decode" and "encode", other methods are available as well. For instance, "name()" returns the canonical name of the encoding object.

  find_encoding("latin1")->name; # iso-8859-1

See Encode::Encoding for details.

from_to

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

Converts in-place data between two encodings. The data in $octets must be encoded as octets and not as characters in Perl's internal format. For example, to convert ISO-8859-1 data into Microsoft's CP1250 encoding:

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

and to convert it back:

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

Because the conversion happens in place, the data to be converted cannot be a string constant: it must be a scalar variable.

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

CAVEAT: The following operations may look the same, but are not:

  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 string, but only #2 turns the UTF8 flag on. #1 is equivalent to:

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

See "The UTF8 flag" below.

Also note that:

  from_to($octets, $from, $to, $check);

is equivalent t:o

  $octets = encode($to, decode($from, $octets), $check);

Yes, it does not respect the $check during decoding. It is deliberately done that way. If you need minute control, use "decode" followed by "encode" as follows:

  $octets = encode($to, decode($from, $octets, $check_from), $check_to);

encode_utf8

  $octets = encode_utf8($string);

Equivalent to "$octets = encode("utf8", $string)". The characters in $string are encoded in Perl's internal format, and the result is returned as a sequence of octets. Because all possible characters in Perl have a (loose, not strict) UTF-8 representation, this function cannot fail.

decode_utf8

  $string = decode_utf8($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 logical characters. Because not all sequences of octets are valid UTF-8, it is quite possible for this function to fail. For CHECK, see "Handling Malformed Data".

Listing available encodings¶

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

Returns a list of canonical names of available encodings that have already been loaded. To get a list of all available encodings including those that have not yet been loaded, 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 an encoding object.

Before you do that, first make sure the alias is nonexistent using "resolve_alias()", which returns the canonical name thereof. For example:

  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 be imported via "use Encode qw(resolve_alias)".

See Encode::Alias for details.

Finding IANA Character Set Registry names¶

The canonical name of a given encoding does not necessarily agree with IANA Character Set Registry, commonly seen as "Content-Type: text/plain; charset=WHATEVER". For most cases, the canonical name works, but sometimes it does not, most notably with "utf-8-strict".

As of "Encode" version 2.21, a new method "mime_name()" is therefore added.

  use Encode;
  my $enc = find_encoding("UTF-8");
  warn $enc->name;      # utf-8-strict
  warn $enc->mime_name; # UTF-8

See also: Encode::Encoding

List of CHECK values¶

FB_DEFAULT

  I<CHECK> = Encode::FB_DEFAULT ( == 0)

If CHECK is 0, encoding and decoding replace any malformed character with a substitution character. When you encode, SUBCHAR is used. When you decode, the Unicode REPLACEMENT CHARACTER, code point U+FFFD, is used. If the data is supposed to be UTF-8, an optional lexical warning of warning category "utf8" is given.

FB_CROAK

  I<CHECK> = Encode::FB_CROAK ( == 1)

If CHECK is 1, methods immediately die with an error message. Therefore, when CHECK is 1, you should trap exceptions with "eval{}", unless you really want to let it "die".

FB_QUIET

  I<CHECK> = Encode::FB_QUIET

If CHECK is set to "Encode::FB_QUIET", encoding and decoding immediately return the portion of the data that has been processed so far when an error occurs. The data argument is overwritten with everything after that point; that is, the unprocessed portion of the data. This is handy when you have to call "decode" repeatedly in the case where your source data may contain partial multi-byte character sequences, (that is, you are reading with a fixed-width buffer). Here's some sample code to do exactly that:

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

FB_WARN

  I<CHECK> = Encode::FB_WARN

This is the same as "FB_QUIET" above, except that instead of being silent on errors, it issues a warning. This is handy for when you are debugging.

FB_PERLQQ FB_HTMLCREF FB_XMLCREF

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 the "Encode::XS" module, "CHECK" "==" "Encode::FB_PERLQQ" puts "encode" and "decode" into "perlqq" fallback mode.

When you decode, "\xHH" is inserted for a malformed character, where HH is the hex representation of the octet that could not be decoded to utf8. When you encode, "\x{HHHH}" will be inserted, where HHHH is the Unicode code point (in any number of hex digits) of the character that cannot be found in the character repertoire of the encoding.

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

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

The bitmask

These modes are all actually set via a bitmask. Here is how the "FB_XXX" constants are laid out. You can import the "FB_XXX" constants via "use Encode qw(:fallbacks)", and you can import the generic bitmask constants 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

LEAVE_SRC

  Encode::LEAVE_SRC

If the "Encode::LEAVE_SRC" bit is not set but CHECK is set, then the source string to encode() or decode() will be overwritten in place. If you're not interested in this, then bitwise-OR it with the bitmask.

coderef for CHECK¶

As of "Encode" 2.12, "CHECK" can also be a code reference which takes the ordinal value of the unmapped character as an argument and returns a string that 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}".

Messing with Perl's Internals¶

The following API uses parts of Perl's internals in the current implementation. As such, they are efficient but may change in a future release.

is_utf8

  is_utf8(STRING [, CHECK])

[INTERNAL] Tests whether the UTF8 flag is turned on in the STRING. If CHECK is true, also checks whether STRING contains well-formed UTF-8. Returns true if successful, false otherwise.

As of Perl 5.8.1, utf8 also has the "utf8::is_utf8" function.

_utf8_on

  _utf8_on(STRING)

[INTERNAL] Turns the STRING's internal UTF8 flag on. The STRING is not checked for containing only well-formed UTF-8. Do not use this unless you know with absolute certainty that the STRING holds only well-formed UTF-8. Returns the previous state of the UTF8 flag (so please don't treat the return value as indicating success or failure), or "undef" if STRING is not a string.

NOTE: For security reasons, this function does not work on tainted values.

_utf8_off

  _utf8_off(STRING)

[INTERNAL] Turns the STRING's internal UTF8 flag off. Do not use frivolously. Returns the previous state of the UTF8 flag, or "undef" if STRING is not a string. Do not treat the return value as indicative of success or failure, because that isn't what it means: it is only the previous setting.

NOTE: For security reasons, this function does not work on tainted values.