encode.3

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.\" ========================================================================
.\"
.IX Title "Encode 3"
.TH Encode 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Encode \- character encodings
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Encode;
.Ve
.Sh "Table of Contents"
.IX Subsection "Table of Contents"
Encode consists of a collection of modules whose details are too big
to fit in one document.  This \s-1POD\s0 itself explains the top-level APIs
and general topics at a glance.  For other topics and more details,
see the PODs below:
.PP
.Vb 10
\&  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
\&  \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`Encode\*(C'\fR module provides the interfaces between Perl's strings
and the rest of the system.  Perl strings are sequences of
\&\fBcharacters\fR.
.PP
The repertoire of characters that Perl can represent is at least that
defined by the Unicode Consortium. On most platforms the ordinal
values of the characters (as returned by \f(CW\*(C`ord(ch)\*(C'\fR) is the \*(L"Unicode
codepoint\*(R" for the character (the exceptions are those platforms where
the legacy encoding is some variant of \s-1EBCDIC\s0 rather than a super-set
of \s-1ASCII\s0 \- see perlebcdic).
.PP
Traditionally, computer data has been moved around in 8\-bit chunks
often called \*(L"bytes\*(R". These chunks are also known as \*(L"octets\*(R" in
networking standards. Perl is widely used to manipulate data of many
types \- not only strings of characters representing human or computer
languages but also \*(L"binary\*(R" data being the machine's representation of
numbers, pixels in an image \- or just about anything.
.PP
When Perl is processing \*(L"binary data\*(R", the programmer wants Perl to
process \*(L"sequences of bytes\*(R". This is not a problem for Perl \- as a
byte has 256 possible values, it easily fits in Perl's much larger
\&\*(L"logical character\*(R".
.Sh "\s-1TERMINOLOGY\s0"
.IX Subsection "TERMINOLOGY"
.IP "\(bu" 2
\&\fIcharacter\fR: a character in the range 0..(2**32\-1) (or more).
(What Perl's strings are made of.)
.IP "\(bu" 2
\&\fIbyte\fR: a character in the range 0..255
(A special case of a Perl character.)
.IP "\(bu" 2
\&\fIoctet\fR: 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.)
.SH "PERL ENCODING API"
.IX Header "PERL ENCODING API"
.ie n .IP "$octets\fR  = encode(\s-1ENCODING\s0, \f(CW$string [, \s-1CHECK\s0])" 2
.el .IP "\f(CW$octets\fR  = encode(\s-1ENCODING\s0, \f(CW$string\fR [, \s-1CHECK\s0])" 2
.IX Item "$octets  = encode(ENCODING, $string [, CHECK])"
Encodes a string from Perl's internal form into \fI\s-1ENCODING\s0\fR and returns
a sequence of octets.  \s-1ENCODING\s0 can be either a canonical name or
an alias.  For encoding names and aliases, see \*(L"Defining Aliases\*(R".
For \s-1CHECK\s0, see \*(L"Handling Malformed Data\*(R".
.Sp
For example, to convert a string from Perl's internal format to
iso\-8859\-1 (also known as Latin1),
.Sp
.Vb 1
\&  $octets = encode("iso\-8859\-1", $string);
.Ve
.Sp
\&\fB\s-1CAVEAT\s0\fR: When you run \f(CW\*(C`$octets = encode("utf8", $string)\*(C'\fR, then
\&\f(CW$octets\fR \fBmay not be equal to\fR \f(CW$string\fR.  Though they both contain the
same data, the \s-1UTF8\s0 flag for \f(CW$octets\fR is \fBalways\fR off.  When you
encode anything, \s-1UTF8\s0 flag of the result is always off, even when it
contains completely valid utf8 string. See \*(L"The \s-1UTF8\s0 flag\*(R" below.
.Sp
If the \f(CW$string\fR is \f(CW\*(C`undef\*(C'\fR then \f(CW\*(C`undef\*(C'\fR is returned.
.ie n .IP "$string\fR = decode(\s-1ENCODING\s0, \f(CW$octets [, \s-1CHECK\s0])" 2
.el .IP "\f(CW$string\fR = decode(\s-1ENCODING\s0, \f(CW$octets\fR [, \s-1CHECK\s0])" 2
.IX Item "$string = decode(ENCODING, $octets [, CHECK])"
Decodes a sequence of octets assumed to be in \fI\s-1ENCODING\s0\fR into Perl's
internal form and returns the resulting string.  As in \fIencode()\fR,
\&\s-1ENCODING\s0 can be either a canonical name or an alias. For encoding names
and aliases, see \*(L"Defining Aliases\*(R".  For \s-1CHECK\s0, see
\&\*(L"Handling Malformed Data\*(R".
.Sp
For example, to convert \s-1ISO\-8859\-1\s0 data to a string in Perl's internal format:
.Sp
.Vb 1
\&  $string = decode("iso\-8859\-1", $octets);
.Ve
.Sp
\&\fB\s-1CAVEAT\s0\fR: When you run \f(CW\*(C`$string = decode("utf8", $octets)\*(C'\fR, then \f(CW$string\fR
\&\fBmay not be equal to\fR \f(CW$octets\fR.  Though they both contain the same data,
the \s-1UTF8\s0 flag for \f(CW$string\fR is on unless \f(CW$octets\fR entirely consists of
\&\s-1ASCII\s0 data (or \s-1EBCDIC\s0 on \s-1EBCDIC\s0 machines).  See \*(L"The \s-1UTF8\s0 flag\*(R"
below.
.Sp
If the \f(CW$string\fR is \f(CW\*(C`undef\*(C'\fR then \f(CW\*(C`undef\*(C'\fR is returned.
.IP "[$obj =] find_encoding(\s-1ENCODING\s0)" 2
.IX Item "[$obj =] find_encoding(ENCODING)"
Returns the \fIencoding object\fR corresponding to \s-1ENCODING\s0.  Returns
undef if no matching \s-1ENCODING\s0 is find.
.Sp
This object is what actually does the actual (en|de)coding.
.Sp
.Vb 1
\&  $utf8 = decode($name, $bytes);
.Ve
.Sp
is in fact
.Sp
.Vb 5
\&  $utf8 = do{
\&    $obj = find_encoding($name);
\&    croak qq(encoding "$name" not found) unless ref $obj;
\&    $obj\->decode($bytes)
\&  };
.Ve
.Sp
with more error checking.
.Sp
Therefore you can save time by reusing this object as follows;
.Sp
.Vb 5
\&  my $enc = find_encoding("iso\-8859\-1");
\&  while(<>){
\&     my $utf8 = $enc\->decode($_);
\&     # and do someting with $utf8;
\&  }
.Ve
.Sp
Besides \f(CW\*(C`\->decode\*(C'\fR and \f(CW\*(C`\->encode\*(C'\fR, other methods are
available as well.  For instance, \f(CW\*(C`\-> name\*(C'\fR returns the canonical
name of the encoding object.
.Sp
.Vb 1
\&  find_encoding("latin1")\->name; # iso\-8859\-1
.Ve
.Sp
See Encode::Encoding for details.
.IP "[$length =] from_to($octets, \s-1FROM_ENC\s0, \s-1TO_ENC\s0 [, \s-1CHECK\s0])" 2
.IX Item "[$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])"
Converts \fBin-place\fR data between two encodings. The data in \f(CW$octets\fR
must be encoded as octets and not as characters in Perl's internal
format. For example, to convert \s-1ISO\-8859\-1\s0 data to Microsoft's \s-1CP1250\s0
encoding:
.Sp
.Vb 1
\&  from_to($octets, "iso\-8859\-1", "cp1250");
.Ve
.Sp
and to convert it back:
.Sp
.Vb 1
\&  from_to($octets, "cp1250", "iso\-8859\-1");
.Ve
.Sp
Note that because the conversion happens in place, the data to be
converted cannot be a string constant; it must be a scalar variable.
.Sp
\&\fIfrom_to()\fR returns the length of the converted string in octets on
success, \fIundef\fR on error.
.Sp
\&\fB\s-1CAVEAT\s0\fR: The following operations look the same but are not quite so;
.Sp
.Vb 2
\&  from_to($data, "iso\-8859\-1", "utf8"); #1
\&  $data = decode("iso\-8859\-1", $data);  #2
.Ve
.Sp
Both #1 and #2 make \f(CW$data\fR consist of a completely valid \s-1UTF\-8\s0 string
but only #2 turns \s-1UTF8\s0 flag on.  #1 is equivalent to
.Sp
.Vb 1
\&  $data = encode("utf8", decode("iso\-8859\-1", $data));
.Ve
.Sp
See \*(L"The \s-1UTF8\s0 flag\*(R" below.
.Sp
Also note that
.Sp
.Vb 1
\&  from_to($octets, $from, $to, $check);
.Ve
.Sp
is equivalent to
.Sp
.Vb 1
\&  $octets = encode($to, decode($from, $octets), $check);
.Ve
.Sp
Yes, it does not respect the \f(CW$check\fR during decoding.  It is
deliberately done that way.  If you need minute control, \f(CW\*(C`decode\*(C'\fR
then \f(CW\*(C`encode\*(C'\fR as follows;
.Sp
.Vb 1
\&  $octets = encode($to, decode($from, $octets, $check_from), $check_to);
.Ve
.ie n .IP "$octets = encode_utf8($string);" 2
.el .IP "\f(CW$octets\fR = encode_utf8($string);" 2
.IX Item "$octets = encode_utf8($string);"
Equivalent to \f(CW\*(C`$octets = encode("utf8", $string);\*(C'\fR The characters
that comprise \f(CW$string\fR are encoded in Perl's internal format and the
result is returned as a sequence of octets. All possible
characters have a \s-1UTF\-8\s0 representation so this function cannot fail.
.ie n .IP "$string = decode_utf8($octets [, \s-1CHECK\s0]);" 2
.el .IP "\f(CW$string\fR = decode_utf8($octets [, \s-1CHECK\s0]);" 2
.IX Item "$string = decode_utf8($octets [, CHECK]);"
equivalent to \f(CW\*(C`$string = decode("utf8", $octets [, CHECK])\*(C'\fR.
The sequence of octets represented by
\&\f(CW$octets\fR is decoded from \s-1UTF\-8\s0 into a sequence of logical
characters. Not all sequences of octets form valid \s-1UTF\-8\s0 encodings, so
it is possible for this call to fail.  For \s-1CHECK\s0, see
\&\*(L"Handling Malformed Data\*(R".
.Sh "Listing available encodings"
.IX Subsection "Listing available encodings"
.Vb 2
\&  use Encode;
\&  @list = Encode\->encodings();
.Ve
.PP
Returns a list of the canonical names of the available encodings that
are loaded.  To get a list of all available encodings including the
ones that are not loaded yet, say
.PP
.Vb 1
\&  @all_encodings = Encode\->encodings(":all");
.Ve
.PP
Or you can give the name of a specific module.
.PP
.Vb 1
\&  @with_jp = Encode\->encodings("Encode::JP");