Initial commit of OpenSPARC T2 architecture model.

[OpenSPARC-T2-SAM] / sam-t2 / devtools / v8plus / man / man3 / Encode::Guess.3

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.\" ========================================================================
.\"
.IX Title "Encode::Guess 3"
.TH Encode::Guess 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide"
.SH "NAME"
Encode::Guess \-\- Guesses encoding from data
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  # if you are sure $data won't contain anything bogus
.Ve
.PP
.Vb 4
\&  use Encode;
\&  use Encode::Guess qw/euc-jp shiftjis 7bit-jis/;
\&  my $utf8 = decode("Guess", $data);
\&  my $data = encode("Guess", $utf8);   # this doesn't work!
.Ve
.PP
.Vb 7
\&  # more elaborate way
\&  use Encode::Guess;
\&  my $enc = guess_encoding($data, qw/euc-jp shiftjis 7bit-jis/);
\&  ref($enc) or die "Can't guess: $enc"; # trap error this way
\&  $utf8 = $enc->decode($data);
\&  # or
\&  $utf8 = decode($enc->name, $data)
.Ve
.SH "ABSTRACT"
.IX Header "ABSTRACT"
Encode::Guess enables you to guess in what encoding a given data is
encoded, or at least tries to.  
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
By default, it checks only ascii, utf8 and \s-1UTF\-16/32\s0 with \s-1BOM\s0.
.PP
.Vb 1
\&  use Encode::Guess; # ascii/utf8/BOMed UTF
.Ve
.PP
To use it more practically, you have to give the names of encodings to
check (\fIsuspects\fR as follows).  The name of suspects can either be
canonical names or aliases.
.PP
\&\s-1CAVEAT:\s0 Unlike \s-1UTF\-\s0(16|32), \s-1BOM\s0 in utf8 is \s-1NOT\s0 \s-1AUTOMATICALLY\s0 \s-1STRIPPED\s0.
.PP
.Vb 2
\& # tries all major Japanese Encodings as well
\&  use Encode::Guess qw/euc-jp shiftjis 7bit-jis/;
.Ve
.PP
If the \f(CW$Encode::Guess::NoUTFAutoGuess\fR variable is set to a true
value, no heuristics will be applied to \s-1UTF8/16/32\s0, and the result
will be limited to the suspects and \f(CW\*(C`ascii\*(C'\fR.
.IP "Encode::Guess\->set_suspects" 4
.IX Item "Encode::Guess->set_suspects"
You can also change the internal suspects list via \f(CW\*(C`set_suspects\*(C'\fR
method. 
.Sp
.Vb 2
\&  use Encode::Guess;
\&  Encode::Guess->set_suspects(qw/euc-jp shiftjis 7bit-jis/);
.Ve
.IP "Encode::Guess\->add_suspects" 4
.IX Item "Encode::Guess->add_suspects"
Or you can use \f(CW\*(C`add_suspects\*(C'\fR method.  The difference is that
\&\f(CW\*(C`set_suspects\*(C'\fR flushes the current suspects list while
\&\f(CW\*(C`add_suspects\*(C'\fR adds.
.Sp
.Vb 5
\&  use Encode::Guess;
\&  Encode::Guess->add_suspects(qw/euc-jp shiftjis 7bit-jis/);
\&  # now the suspects are euc-jp,shiftjis,7bit-jis, AND
\&  # euc-kr,euc-cn, and big5-eten
\&  Encode::Guess->add_suspects(qw/euc-kr euc-cn big5-eten/);
.Ve
.ie n .IP "Encode::decode(""Guess"" ...)" 4
.el .IP "Encode::decode(``Guess'' ...)" 4
.IX Item "Encode::decode(Guess ...)"
When you are content with suspects list, you can now
.Sp
.Vb 1
\&  my $utf8 = Encode::decode("Guess", $data);
.Ve
.IP "Encode::Guess\->guess($data)" 4
.IX Item "Encode::Guess->guess($data)"
But it will croak if:
.RS 4
.IP "*" 4
Two or more suspects remain
.IP "*" 4
No suspects left
.RE
.RS 4
.Sp
So you should instead try this;
.Sp
.Vb 1
\&  my $decoder = Encode::Guess->guess($data);
.Ve
.Sp
On success, \f(CW$decoder\fR is an object that is documented in
Encode::Encoding.  So you can now do this;
.Sp
.Vb 1
\&  my $utf8 = $decoder->decode($data);
.Ve
.Sp
On failure, \f(CW$decoder\fR now contains an error message so the whole thing
would be as follows;
.Sp
.Vb 3
\&  my $decoder = Encode::Guess->guess($data);
\&  die $decoder unless ref($decoder);
\&  my $utf8 = $decoder->decode($data);
.Ve
.RE
.IP "guess_encoding($data, [, \fIlist of suspects\fR])" 4
.IX Item "guess_encoding($data, [, list of suspects])"
You can also try \f(CW\*(C`guess_encoding\*(C'\fR function which is exported by
default.  It takes \f(CW$data\fR to check and it also takes the list of
suspects by option.  The optional suspect list is \fInot reflected\fR to
the internal suspects list.
.Sp
.Vb 5
\&  my $decoder = guess_encoding($data, qw/euc-jp euc-kr euc-cn/);
\&  die $decoder unless ref($decoder);
\&  my $utf8 = $decoder->decode($data);
\&  # check only ascii and utf8
\&  my $decoder = guess_encoding($data);
.Ve
.SH "CAVEATS"
.IX Header "CAVEATS"
.IP "\(bu" 4
Because of the algorithm used, \s-1ISO\-8859\s0 series and other single-byte
encodings do not work well unless either one of \s-1ISO\-8859\s0 is the only
one suspect (besides ascii and utf8).
.Sp
.Vb 5
\&  use Encode::Guess;
\&  # perhaps ok
\&  my $decoder = guess_encoding($data, 'latin1');
\&  # definitely NOT ok
\&  my $decoder = guess_encoding($data, qw/latin1 greek/);
.Ve
.Sp
The reason is that Encode::Guess guesses encoding by trial and error.
It first splits \f(CW$data\fR into lines and tries to decode the line for each
suspect.  It keeps it going until all but one encoding is eliminated
out of suspects list.  \s-1ISO\-8859\s0 series is just too successful for most
cases (because it fills almost all code points in \ex00\-\exff).
.IP "\(bu" 4
Do not mix national standard encodings and the corresponding vendor
encodings.
.Sp
.Vb 3
\&  # a very bad idea
\&  my $decoder
\&     = guess_encoding($data, qw/shiftjis MacJapanese cp932/);
.Ve
.Sp
The reason is that vendor encoding is usually a superset of national
standard so it becomes too ambiguous for most cases.
.IP "\(bu" 4
On the other hand, mixing various national standard encodings
automagically works unless \f(CW$data\fR is too short to allow for guessing.
.Sp
.Vb 6
\& # This is ok if $data is long enough
\& my $decoder =  
\&  guess_encoding($data, qw/euc-cn
\&                           euc-jp shiftjis 7bit-jis
\&                           euc-kr
\&                           big5-eten/);
.Ve
.IP "\(bu" 4
\&\s-1DO\s0 \s-1NOT\s0 \s-1PUT\s0 \s-1TOO\s0 \s-1MANY\s0 \s-1SUSPECTS\s0!  Don't you try something like this!
.Sp
.Vb 2
\&  my $decoder = guess_encoding($data, 
\&                               Encode->encodings(":all"));
.Ve
.PP
It is, after all, just a guess.  You should alway be explicit when it
comes to encodings.  But there are some, especially Japanese,
environment that guess-coding is a must.  Use this module with care. 
.SH "TO DO"
.IX Header "TO DO"
Encode::Guess does not work on \s-1EBCDIC\s0 platforms.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Encode, Encode::Encoding