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.\" ========================================================================
.\"
.IX Title "Encode::Guess 3perl"
.TH Encode::Guess 3perl 2023-11-30 "perl v5.38.2" "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::Guess \-\- Guesses encoding from data
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&  # if you are sure $data won\*(Aqt contain anything bogus
\&
\&  use Encode;
\&  use Encode::Guess qw/euc\-jp shiftjis 7bit\-jis/;
\&  my $utf8 = decode("Guess", $data);
\&  my $data = encode("Guess", $utf8);   # this doesn\*(Aqt work!
\&
\&  # more elaborate way
\&  use Encode::Guess;
\&  my $enc = guess_encoding($data, qw/euc\-jp shiftjis 7bit\-jis/);
\&  ref($enc) or die "Can\*(Aqt guess: $enc"; # trap error this way
\&  $utf8 = $enc\->decode($data);
\&  # or
\&  $utf8 = decode($enc\->name, $data)
.Ve
.SH ABSTRACT
.IX Header "ABSTRACT"
Encode::Guess enables you to guess in what encoding a given data is
encoded, or at least tries to.
.SH DESCRIPTION
.IX Header "DESCRIPTION"
By default, it checks only ascii, utf8 and UTF\-16/32 with BOM.
.PP
.Vb 1
\&  use Encode::Guess; # ascii/utf8/BOMed UTF
.Ve
.PP
To use it more practically, you have to give the names of encodings to
check (\fIsuspects\fR as follows).  The name of suspects can either be
canonical names or aliases.
.PP
CAVEAT: Unlike UTF\-(16|32), BOM in utf8 is NOT AUTOMATICALLY STRIPPED.
.PP
.Vb 2
\& # tries all major Japanese Encodings as well
\&  use Encode::Guess qw/euc\-jp shiftjis 7bit\-jis/;
.Ve
.PP
If the \f(CW$Encode::Guess::NoUTFAutoGuess\fR variable is set to a true
value, no heuristics will be applied to UTF8/16/32, 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
.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 \(bu 4
Two or more suspects remain
.IP \(bu 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, utf8 and UTF\-(16|32) with BOM
\&  my $decoder = guess_encoding($data);
.Ve
.SH CAVEATS
.IX Header "CAVEATS"
.IP \(bu 4
Because of the algorithm used, ISO\-8859 series and other single-byte
encodings do not work well unless either one of ISO\-8859 is the only
one suspect (besides ascii and utf8).
.Sp
.Vb 5
\&  use Encode::Guess;
\&  # perhaps ok
\&  my $decoder = guess_encoding($data, \*(Aqlatin1\*(Aq);
\&  # 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.  ISO\-8859 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
DO NOT PUT TOO MANY SUSPECTS!  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 EBCDIC platforms.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Encode, Encode::Encoding