encoding - allows you to write your script in non-ascii or non-utf8 |
encoding - allows you to write your script in non-ascii or non-utf8
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; use utf8; # now you can use kanji identifiers -- in euc-jp!
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.
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/;
The encoding pragma also modifies the filehandle disciplines 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.
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.
Note that non-STD file handles remain unaffected. Use use open
or
binmode
to change disciplines of those.
STDIN => ENCNAME
form. In this case, you cannot omit the
first ENCNAME. STDIN => undef
turns the IO transcoding
completely off.
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.
Because of this nature, the use of this pragma inside the module is
strongly discouraged (because the influence of this pragma lasts not
only for the module but the script that uses). But if you have to,
make sure you say no encoding
at the end of the module so you
contain the influence of the pragma within the module.
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. As of 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
$kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;
utf8 euc-jp charnames::viacode() ----------------------------------------- \x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A \x{3093} \xA4\xF3 HIRAGANA LETTER N \x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A \x{30f3} \xA5\xF3 KATAKANA LETTER N
You can, however, achieve the same as simply as follows;
use encoding 'euc-jp'; # .... eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };
Note the tr//
expression is surronded by qq{}
. The idea behind
is the same as classic idiom that makes tr///
'interpolate'.
tr/$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. In future version of perl, this counter-intuitive behaviour
of tr///
will be fixed so eval qq{}
trick will be unneccesary.
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.
In other words, the same restriction as with Jperl applies.
If you dare to experiment, however, you can try the Filter option.
qq()
and qr()), this
will apply a source filter to the entire source code. In this case,
STDIN and STDOUT remain untouched.
What does this mean? Your source code behaves as if it is written in
UTF-8. 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.
To make your script in legacy encoding work with minimum effort, do not use Filter=>1.
use encoding "iso 8859-7";
# \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.
$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;
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.
The encoding pragma is not supported on EBCDIC platforms. (Porters who are willing and able to remove this limitation are welcome.)
the perlunicode manpage, the Encode manpage, the open manpage, the Filter::Util::Call manpage,
Ch. 15 of Programming Perl (3rd Edition)
by Larry Wall, Tom Christiansen, Jon Orwant;
O'Reilly & Associates; ISBN 0-596-00027-8
encoding - allows you to write your script in non-ascii or non-utf8 |