# 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';
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 supported 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.
Changing PerlIO layers of STDIN and STDOUT to the encoding specified.
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.
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 encoding 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 $string
is three octets when interpreted as Latin-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.
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.
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.
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If no encoding is specified, the environment variable PERL_ENCODING
is consulted. If no encoding can be found, the error Unknown encoding 'I<ENCNAME>' will be thrown.
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.
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When ${^UNICODE} exists and non-zero, these options will completely
ignored. ${^UNICODE} is a variable introduced in perl 5.8.1. See
perlrun see perlvar/``${^UNICODE}'' and perlrun/``-C'' for
details (perl 5.8.1 and later).
This turns the encoding pragma into a source filter. 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.
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.
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;
# 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.
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 characters 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 encoding in quotes and
regexes.
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,
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.
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.
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.
This pragma doesn't work well with format because PerlIO does not
get along very well with it. When format contains non-ascii
characters it prints funny or gets ``wide character warnings''.
To understand it, try the code below.
# 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 binmode, 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 consider such things as character
width (i.e. double-width for ideographs) and directions (i.e. BIDI for
Arabic and Hebrew).
If the platform supports the langinfo(CODESET) interface, the codeset
returned is used as the default encoding for the open pragma.
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.
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.
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