ext::Encode::encoPerl(Programmers Refereext::Encode::encoding(3p)NAMEencoding - allows you to write your script in non-ascii or
non-utf8
SYNOPSIS
use encoding "greek"; # Perl like Greek to you?
use encoding "euc-jp"; # Jperl!
# or you can even do this if your shell supports your native encoding
perl -Mencoding=latin2 -e '...' # Feeling centrally European?
perl -Mencoding=euc-kr -e '...' # Or Korean?
# more control
# A simple euc-cn => utf-8 converter
use encoding "euc-cn", STDOUT => "utf8"; while(<>){print};
# "no encoding;" supported (but not scoped!)
no encoding;
# an alternate way, Filter
use encoding "euc-jp", Filter=>1;
# now you can use kanji identifiers -- in euc-jp!
# switch on locale -
# note that this probably means that unless you have a complete control
# over the environments the application is ever going to be run, you should
# NOT use the feature of encoding pragma allowing you to write your script
# in any recognized encoding because changing locale settings will wreck
# the script; you can of course still use the other features of the pragma.
use encoding ':locale';
ABSTRACT
Let's start with a bit of history: Perl 5.6.0 introduced
Unicode support. You could apply "substr()" and regexes
even to complex CJK characters -- so long as the script was
written in UTF-8. But back then, text editors that sup-
ported UTF-8 were still rare and many users instead chose to
write scripts in legacy encodings, giving up a whole new
feature of Perl 5.6.
Rewind to the future: starting from perl 5.8.0 with the
encoding pragma, you can write your script in any encoding
you like (so long as the "Encode" module supports it) and
still enjoy Unicode support. This pragma achieves that by
doing the following:
+ Internally converts all literals ("q//,qq//,qr//,qw///,
qx//") from the encoding specified to utf8. In Perl
5.8.1 and later, literals in "tr///" and "DATA" pseudo-
filehandle are also converted.
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+ Changing PerlIO layers of "STDIN" and "STDOUT" to the
encoding
specified.
Literal Conversions
You can write code in EUC-JP as follows:
my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
#<-char-><-char-> # 4 octets
s/\bCamel\b/$Rakuda/;
And with "use encoding "euc-jp"" in effect, it is the same
thing as the code in UTF-8:
my $Rakuda = "\x{99F1}\x{99DD}"; # two Unicode Characters
s/\bCamel\b/$Rakuda/;
PerlIO layers for "STD(IN|OUT)"
The encoding pragma also modifies the filehandle layers of
STDIN and STDOUT to the specified encoding. Therefore,
use encoding "euc-jp";
my $message = "Camel is the symbol of perl.\n";
my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
$message =~ s/\bCamel\b/$Rakuda/;
print $message;
Will print "\xF1\xD1\xF1\xCC is the symbol of perl.\n", not
"\x{99F1}\x{99DD} is the symbol of perl.\n".
You can override this by giving extra arguments; see below.
Implicit upgrading for byte strings
By default, if strings operating under byte semantics and
strings with Unicode character data are concatenated, the
new string will be created by decoding the byte strings as
ISO 8859-1 (Latin-1).
The encoding pragma changes this to use the specified encod-
ing instead. For example:
use encoding 'utf8';
my $string = chr(20000); # a Unicode string
utf8::encode($string); # now it's a UTF-8 encoded byte string
# concatenate with another Unicode string
print length($string . chr(20000));
Will print 2, because $string is upgraded as UTF-8. Without
"use encoding 'utf8';", it will print 4 instead, since
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$string is three octets when interpreted as Latin-1.
FEATURES THAT REQUIRE 5.8.1
Some of the features offered by this pragma requires perl
5.8.1. Most of these are done by Inaba Hiroto. Any other
features and changes are good for 5.8.0.
"NON-EUC" doublebyte encodings
Because perl needs to parse script before applying this
pragma, such encodings as Shift_JIS and Big-5 that may
contain '\' (BACKSLASH; \x5c) in the second byte fails
because the second byte may accidentally escape the
quoting character that follows. Perl 5.8.1 or later
fixes this problem.
tr//
"tr//" was overlooked by Perl 5 porters when they
released perl 5.8.0 See the section below for details.
DATA pseudo-filehandle
Another feature that was overlooked was "DATA".
USAGE
use encoding [ENCNAME] ;
Sets the script encoding to ENCNAME. And unless
${^UNICODE} exists and non-zero, PerlIO layers of STDIN
and STDOUT are set to ":encoding(ENCNAME)".
Note that STDERR WILL NOT be changed.
Also note that non-STD file handles remain unaffected.
Use "use open" or "binmode" to change layers of those.
If no encoding is specified, the environment variable
PERL_ENCODING is consulted. If no encoding can be
found, the error "Unknown encoding 'ENCNAME'" will be
thrown.
use encoding ENCNAME [ STDIN => ENCNAME_IN ...] ;
You can also individually set encodings of STDIN and
STDOUT via the "STDIN => ENCNAME" form. In this case,
you cannot omit the first ENCNAME. "STDIN => undef"
turns the IO transcoding completely off.
When ${^UNICODE} exists and non-zero, these options will
completely ignored. ${^UNICODE} is a variable intro-
duced in perl 5.8.1. See perlrun see "${^UNICODE}" in
perlvar and "-C" in perlrun for details (perl 5.8.1 and
later).
use encoding ENCNAME Filter=>1;
This turns the encoding pragma into a source filter.
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While the default approach just decodes interpolated
literals (in qq() and qr()), this will apply a source
filter to the entire source code. See "The Filter
Option" below for details.
no encoding;
Unsets the script encoding. The layers of STDIN, STDOUT
are reset to ":raw" (the default unprocessed raw stream
of bytes).
The Filter Option
The magic of "use encoding" is not applied to the names of
identifiers. In order to make "${"\x{4eba}"}++" ($human++,
where human is a single Han ideograph) work, you still need
to write your script in UTF-8 -- or use a source filter.
That's what 'Filter=>1' does.
What does this mean? Your source code behaves as if it is
written in UTF-8 with 'use utf8' in effect. So even if your
editor only supports Shift_JIS, for example, you can still
try examples in Chapter 15 of "Programming Perl, 3rd Ed.".
For instance, you can use UTF-8 identifiers.
This option is significantly slower and (as of this writing)
non-ASCII identifiers are not very stable WITHOUT this
option and with the source code written in UTF-8.
Filter-related changes at Encode version 1.87
+ The Filter option now sets STDIN and STDOUT like non-
filter options. And "STDIN=>ENCODING" and
"STDOUT=>ENCODING" work like non-filter version.
+ "use utf8" is implicitly declared so you no longer have
to "use utf8" to "${"\x{4eba}"}++".
CAVEATS
NOT SCOPED
The pragma is a per script, not a per block lexical. Only
the last "use encoding" or "no encoding" matters, and it
affects the whole script. However, the <no encoding> pragma
is supported and use encoding can appear as many times as
you want in a given script. The multiple use of this pragma
is discouraged.
By the same reason, the use this pragma inside modules is
also discouraged (though not as strongly discouraged as the
case above. See below).
If you still have to write a module with this pragma, be
very careful of the load order. See the codes below;
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# called module
package Module_IN_BAR;
use encoding "bar";
# stuff in "bar" encoding here
1;
# caller script
use encoding "foo"
use Module_IN_BAR;
# surprise! use encoding "bar" is in effect.
The best way to avoid this oddity is to use this pragma
RIGHT AFTER other modules are loaded. i.e.
use Module_IN_BAR;
use encoding "foo";
DO NOT MIX MULTIPLE ENCODINGS
Notice that only literals (string or regular expression)
having only legacy code points are affected: if you mix data
like this
\xDF\x{100}
the data is assumed to be in (Latin 1 and) Unicode, not in
your native encoding. In other words, this will match in
"greek":
"\xDF" =~ /\x{3af}/
but this will not
"\xDF\x{100}" =~ /\x{3af}\x{100}/
since the "\xDF" (ISO 8859-7 GREEK SMALL LETTER IOTA WITH
TONOS) on the left will not be upgraded to "\x{3af}"
(Unicode GREEK SMALL LETTER IOTA WITH TONOS) because of the
"\x{100}" on the left. You should not be mixing your legacy
data and Unicode in the same string.
This pragma also affects encoding of the 0x80..0xFF code
point range: normally characters in that range are left as
eight-bit bytes (unless they are combined with characters
with code points 0x100 or larger, in which case all charac-
ters need to become UTF-8 encoded), but if the "encoding"
pragma is present, even the 0x80..0xFF range always gets
UTF-8 encoded.
After all, the best thing about this pragma is that you
don't have to resort to \x{....} just to spell your name in
a native encoding. So feel free to put your strings in your
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tr/// with ranges
The encoding pragma works by decoding string literals in
"q//,qq//,qr//,qw///, qx//" and so forth. In perl 5.8.0,
this does not apply to "tr///". Therefore,
use encoding 'euc-jp';
#....
$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/;
# -------- -------- -------- --------
Does not work as
$kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;
Legend of characters above
utf8 euc-jp charnames::viacode()-----------------------------------------
\x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A
\x{3093} \xA4\xF3 HIRAGANA LETTER N
\x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A
\x{30f3} \xA5\xF3 KATAKANA LETTER N
This counterintuitive behavior has been fixed in perl 5.8.1.
workaround to tr///;
In perl 5.8.0, you can work around as follows;
use encoding 'euc-jp';
# ....
eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };
Note the "tr//" expression is surrounded by "qq{}". The
idea behind is the same as classic idiom that makes "tr///"
'interpolate'.
tr/$from/$to/; # wrong!
eval qq{ tr/$from/$to/ }; # workaround.
Nevertheless, in case of encoding pragma even "q//" is
affected so "tr///" not being decoded was obviously against
the will of Perl5 Porters so it has been fixed in Perl 5.8.1
or later.
EXAMPLE - Greekperl
use encoding "iso 8859-7";
# \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.
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$a = "\xDF";
$b = "\x{100}";
printf "%#x\n", ord($a); # will print 0x3af, not 0xdf
$c = $a . $b;
# $c will be "\x{3af}\x{100}", not "\x{df}\x{100}".
# chr() is affected, and ...
print "mega\n" if ord(chr(0xdf)) == 0x3af;
# ... ord() is affected by the encoding pragma ...
print "tera\n" if ord(pack("C", 0xdf)) == 0x3af;
# ... as are eq and cmp ...
print "peta\n" if "\x{3af}" eq pack("C", 0xdf);
print "exa\n" if "\x{3af}" cmp pack("C", 0xdf) == 0;
# ... but pack/unpack C are not affected, in case you still
# want to go back to your native encoding
print "zetta\n" if unpack("C", (pack("C", 0xdf))) == 0xdf;
KNOWN PROBLEMS
literals in regex that are longer than 127 bytes
For native multibyte encodings (either fixed or variable
length), the current implementation of the regular
expressions may introduce recoding errors for regular
expression literals longer than 127 bytes.
EBCDIC
The encoding pragma is not supported on EBCDIC plat-
forms. (Porters who are willing and able to remove this
limitation are welcome.)
format
This pragma doesn't work well with format because PerlIO
does not get along very well with it. When format con-
tains non-ascii characters it prints funny or gets "wide
character warnings". To understand it, try the code
below.
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# Save this one in utf8
# replace *non-ascii* with a non-ascii string
my $camel;
format STDOUT =
*non-ascii*@>>>>>>>
$camel
.
$camel = "*non-ascii*";
binmode(STDOUT=>':encoding(utf8)'); # bang!
write; # funny
print $camel, "\n"; # fine
Without binmode this happens to work but without bin-
mode, print() fails instead of write().
At any rate, the very use of format is questionable when
it comes to unicode characters since you have to con-
sider such things as character width (i.e. double-width
for ideographs) and directions (i.e. BIDI for Arabic and
Hebrew).
The Logic of :locale
The logic of ":locale" is as follows:
1. If the platform supports the langinfo(CODESET) inter-
face, the codeset returned is used as the default encod-
ing for the open pragma.
2. If 1. didn't work but we are under the locale pragma,
the environment variables LC_ALL and LANG (in that
order) are matched for encodings (the part after ".", if
any), and if any found, that is used as the default
encoding for the open pragma.
3. If 1. and 2. didn't work, the environment variables
LC_ALL and LANG (in that order) are matched for anything
looking like UTF-8, and if any found, ":utf8" is used as
the default encoding for the open pragma.
If your locale environment variables (LC_ALL, LC_CTYPE,
LANG) contain the strings 'UTF-8' or 'UTF8'
(case-insensitive matching), the default encoding of your
STDIN, STDOUT, and STDERR, and of any subsequent file open,
is UTF-8.
HISTORY
This pragma first appeared in Perl 5.8.0. For features that
require 5.8.1 and better, see above.
The ":locale" subpragma was implemented in 2.01, or Perl
5.8.6.
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ext::Encode::encoPerl(Programmers Refereext::Encode::encoding(3p)SEE ALSO
perlunicode, Encode, open, Filter::Util::Call,
Ch. 15 of "Programming Perl (3rd Edition)" by Larry Wall,
Tom Christiansen, Jon Orwant; O'Reilly & Associates; ISBN
0-596-00027-8
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