encoding(3pm)

1encoding(3pm)          Perl Programmers Reference Guide          encoding(3pm)
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NAME

6       encoding - allows you to write your script in non-ascii or non-utf8
7

SYNOPSIS

9         use encoding "greek";  # Perl like Greek to you?
10         use encoding "euc-jp"; # Jperl!
11
12         # or you can even do this if your shell supports your native encoding
13
14         perl -Mencoding=latin2 -e'...' # Feeling centrally European?
15         perl -Mencoding=euc-kr -e'...' # Or Korean?
16
17         # more control
18
19         # A simple euc-cn => utf-8 converter
20         use encoding "euc-cn", STDOUT => "utf8";  while(<>){print};
21
22         # "no encoding;" supported (but not scoped!)
23         no encoding;
24
25         # an alternate way, Filter
26         use encoding "euc-jp", Filter=>1;
27         # now you can use kanji identifiers -- in euc-jp!
28
29         # switch on locale -
30         # note that this probably means that unless you have a complete control
31         # over the environments the application is ever going to be run, you should
32         # NOT use the feature of encoding pragma allowing you to write your script
33         # in any recognized encoding because changing locale settings will wreck
34         # the script; you can of course still use the other features of the pragma.
35         use encoding ':locale';
36

ABSTRACT

38       Let's start with a bit of history: Perl 5.6.0 introduced Unicode
39       support.  You could apply "substr()" and regexes even to complex CJK
40       characters -- so long as the script was written in UTF-8.  But back
41       then, text editors that supported UTF-8 were still rare and many users
42       instead chose to write scripts in legacy encodings, giving up a whole
43       new feature of Perl 5.6.
44
45       Rewind to the future: starting from perl 5.8.0 with the encoding
46       pragma, you can write your script in any encoding you like (so long as
47       the "Encode" module supports it) and still enjoy Unicode support.  This
48       pragma achieves that by doing the following:
49
50       ·   Internally converts all literals ("q//,qq//,qr//,qw///, qx//") from
51           the encoding specified to utf8.  In Perl 5.8.1 and later, literals
52           in "tr///" and "DATA" pseudo-filehandle are also converted.
53
54       ·   Changing PerlIO layers of "STDIN" and "STDOUT" to the encoding
55            specified.
56
57   Literal Conversions
58       You can write code in EUC-JP as follows:
59
60         my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
61                      #<-char-><-char->   # 4 octets
62         s/\bCamel\b/$Rakuda/;
63
64       And with "use encoding "euc-jp"" in effect, it is the same thing as the
65       code in UTF-8:
66
67         my $Rakuda = "\x{99F1}\x{99DD}"; # two Unicode Characters
68         s/\bCamel\b/$Rakuda/;
69
70   PerlIO layers for "STD(IN|OUT)"
71       The encoding pragma also modifies the filehandle layers of STDIN and
72       STDOUT to the specified encoding.  Therefore,
73
74         use encoding "euc-jp";
75         my $message = "Camel is the symbol of perl.\n";
76         my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
77         $message =~ s/\bCamel\b/$Rakuda/;
78         print $message;
79
80       Will print "\xF1\xD1\xF1\xCC is the symbol of perl.\n", not
81       "\x{99F1}\x{99DD} is the symbol of perl.\n".
82
83       You can override this by giving extra arguments; see below.
84
85   Implicit upgrading for byte strings
86       By default, if strings operating under byte semantics and strings with
87       Unicode character data are concatenated, the new string will be created
88       by decoding the byte strings as ISO 8859-1 (Latin-1).
89
90       The encoding pragma changes this to use the specified encoding instead.
91       For example:
92
93           use encoding 'utf8';
94           my $string = chr(20000); # a Unicode string
95           utf8::encode($string);   # now it's a UTF-8 encoded byte string
96           # concatenate with another Unicode string
97           print length($string . chr(20000));
98
99       Will print 2, because $string is upgraded as UTF-8.  Without "use
100       encoding 'utf8';", it will print 4 instead, since $string is three
101       octets when interpreted as Latin-1.
102
103   Side effects
104       If the "encoding" pragma is in scope then the lengths returned are
105       calculated from the length of $/ in Unicode characters, which is not
106       always the same as the length of $/ in the native encoding.
107
108       This pragma affects utf8::upgrade, but not utf8::downgrade.
109

FEATURES THAT REQUIRE 5.8.1

111       Some of the features offered by this pragma requires perl 5.8.1.  Most
112       of these are done by Inaba Hiroto.  Any other features and changes are
113       good for 5.8.0.
114
115       "NON-EUC" doublebyte encodings
116           Because perl needs to parse script before applying this pragma,
117           such encodings as Shift_JIS and Big-5 that may contain '\'
118           (BACKSLASH; \x5c) in the second byte fails because the second byte
119           may accidentally escape the quoting character that follows.  Perl
120           5.8.1 or later fixes this problem.
121
122       tr//
123           "tr//" was overlooked by Perl 5 porters when they released perl
124           5.8.0 See the section below for details.
125
126       DATA pseudo-filehandle
127           Another feature that was overlooked was "DATA".
128

USAGE

130       use encoding [ENCNAME] ;
131           Sets the script encoding to ENCNAME.  And unless ${^UNICODE} exists
132           and non-zero, PerlIO layers of STDIN and STDOUT are set to
133           ":encoding(ENCNAME)".
134
135           Note that STDERR WILL NOT be changed.
136
137           Also note that non-STD file handles remain unaffected.  Use "use
138           open" or "binmode" to change layers of those.
139
140           If no encoding is specified, the environment variable PERL_ENCODING
141           is consulted.  If no encoding can be found, the error "Unknown
142           encoding 'ENCNAME'" will be thrown.
143
144       use encoding ENCNAME [ STDIN => ENCNAME_IN ...] ;
145           You can also individually set encodings of STDIN and STDOUT via the
146           "STDIN => ENCNAME" form.  In this case, you cannot omit the first
147           ENCNAME.  "STDIN => undef" turns the IO transcoding completely off.
148
149           When ${^UNICODE} exists and non-zero, these options will completely
150           ignored.  ${^UNICODE} is a variable introduced in perl 5.8.1.  See
151           perlrun see "${^UNICODE}" in perlvar and "-C" in perlrun for
152           details (perl 5.8.1 and later).
153
154       use encoding ENCNAME Filter=>1;
155           This turns the encoding pragma into a source filter.  While the
156           default approach just decodes interpolated literals (in qq() and
157           qr()), this will apply a source filter to the entire source code.
158           See "The Filter Option" below for details.
159
160       no encoding;
161           Unsets the script encoding. The layers of STDIN, STDOUT are reset
162           to ":raw" (the default unprocessed raw stream of bytes).
163

The Filter Option

165       The magic of "use encoding" is not applied to the names of identifiers.
166       In order to make "${"\x{4eba}"}++" ($human++, where human is a single
167       Han ideograph) work, you still need to write your script in UTF-8 -- or
168       use a source filter.  That's what 'Filter=>1' does.
169
170       What does this mean?  Your source code behaves as if it is written in
171       UTF-8 with 'use utf8' in effect.  So even if your editor only supports
172       Shift_JIS, for example, you can still try examples in Chapter 15 of
173       "Programming Perl, 3rd Ed.".  For instance, you can use UTF-8
174       identifiers.
175
176       This option is significantly slower and (as of this writing) non-ASCII
177       identifiers are not very stable WITHOUT this option and with the source
178       code written in UTF-8.
179
180   Filter-related changes at Encode version 1.87
181       ·   The Filter option now sets STDIN and STDOUT like non-filter
182           options.  And "STDIN=>ENCODING" and "STDOUT=>ENCODING" work like
183           non-filter version.
184
185       ·   "use utf8" is implicitly declared so you no longer have to "use
186           utf8" to "${"\x{4eba}"}++".
187

CAVEATS

189   NOT SCOPED
190       The pragma is a per script, not a per block lexical.  Only the last
191       "use encoding" or "no encoding" matters, and it affects the whole
192       script.  However, the <no encoding> pragma is supported and use
193       encoding can appear as many times as you want in a given script.  The
194       multiple use of this pragma is discouraged.
195
196       By the same reason, the use this pragma inside modules is also
197       discouraged (though not as strongly discouraged as the case above.  See
198       below).
199
200       If you still have to write a module with this pragma, be very careful
201       of the load order.  See the codes below;
202
203         # called module
204         package Module_IN_BAR;
205         use encoding "bar";
206         # stuff in "bar" encoding here
207         1;
208
209         # caller script
210         use encoding "foo"
211         use Module_IN_BAR;
212         # surprise! use encoding "bar" is in effect.
213
214       The best way to avoid this oddity is to use this pragma RIGHT AFTER
215       other modules are loaded.  i.e.
216
217         use Module_IN_BAR;
218         use encoding "foo";
219
220   DO NOT MIX MULTIPLE ENCODINGS
221       Notice that only literals (string or regular expression) having only
222       legacy code points are affected: if you mix data like this
223
224           \xDF\x{100}
225
226       the data is assumed to be in (Latin 1 and) Unicode, not in your native
227       encoding.  In other words, this will match in "greek":
228
229           "\xDF" =~ /\x{3af}/
230
231       but this will not
232
233           "\xDF\x{100}" =~ /\x{3af}\x{100}/
234
235       since the "\xDF" (ISO 8859-7 GREEK SMALL LETTER IOTA WITH TONOS) on the
236       left will not be upgraded to "\x{3af}" (Unicode GREEK SMALL LETTER IOTA
237       WITH TONOS) because of the "\x{100}" on the left.  You should not be
238       mixing your legacy data and Unicode in the same string.
239
240       This pragma also affects encoding of the 0x80..0xFF code point range:
241       normally characters in that range are left as eight-bit bytes (unless
242       they are combined with characters with code points 0x100 or larger, in
243       which case all characters need to become UTF-8 encoded), but if the
244       "encoding" pragma is present, even the 0x80..0xFF range always gets
245       UTF-8 encoded.
246
247       After all, the best thing about this pragma is that you don't have to
248       resort to \x{....} just to spell your name in a native encoding.  So
249       feel free to put your strings in your encoding in quotes and regexes.
250
251   tr/// with ranges
252       The encoding pragma works by decoding string literals in
253       "q//,qq//,qr//,qw///, qx//" and so forth.  In perl 5.8.0, this does not
254       apply to "tr///".  Therefore,
255
256         use encoding 'euc-jp';
257         #....
258         $kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/;
259         #           -------- -------- -------- --------
260
261       Does not work as
262
263         $kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;
264
265       Legend of characters above
266             utf8     euc-jp   charnames::viacode()
267             -----------------------------------------
268             \x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A
269             \x{3093} \xA4\xF3 HIRAGANA LETTER N
270             \x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A
271             \x{30f3} \xA5\xF3 KATAKANA LETTER N
272
273       This counterintuitive behavior has been fixed in perl 5.8.1.
274
275       workaround to tr///;
276
277       In perl 5.8.0, you can work around as follows;
278
279         use encoding 'euc-jp';
280         #  ....
281         eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };
282
283       Note the "tr//" expression is surrounded by "qq{}".  The idea behind is
284       the same as classic idiom that makes "tr///" 'interpolate'.
285
286          tr/$from/$to/;            # wrong!
287          eval qq{ tr/$from/$to/ }; # workaround.
288
289       Nevertheless, in case of encoding pragma even "q//" is affected so
290       "tr///" not being decoded was obviously against the will of Perl5
291       Porters so it has been fixed in Perl 5.8.1 or later.
292

EXAMPLE - Greekperl

294           use encoding "iso 8859-7";
295
296           # \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.
297
298           $a = "\xDF";
299           $b = "\x{100}";
300
301           printf "%#x\n", ord($a); # will print 0x3af, not 0xdf
302
303           $c = $a . $b;
304
305           # $c will be "\x{3af}\x{100}", not "\x{df}\x{100}".
306
307           # chr() is affected, and ...
308
309           print "mega\n"  if ord(chr(0xdf)) == 0x3af;
310
311           # ... ord() is affected by the encoding pragma ...
312
313           print "tera\n" if ord(pack("C", 0xdf)) == 0x3af;
314
315           # ... as are eq and cmp ...
316
317           print "peta\n" if "\x{3af}" eq  pack("C", 0xdf);
318           print "exa\n"  if "\x{3af}" cmp pack("C", 0xdf) == 0;
319
320           # ... but pack/unpack C are not affected, in case you still
321           # want to go back to your native encoding
322
323           print "zetta\n" if unpack("C", (pack("C", 0xdf))) == 0xdf;
324

KNOWN PROBLEMS

326       literals in regex that are longer than 127 bytes
327           For native multibyte encodings (either fixed or variable length),
328           the current implementation of the regular expressions may introduce
329           recoding errors for regular expression literals longer than 127
330           bytes.
331
332       EBCDIC
333           The encoding pragma is not supported on EBCDIC platforms.  (Porters
334           who are willing and able to remove this limitation are welcome.)
335
336       format
337           This pragma doesn't work well with format because PerlIO does not
338           get along very well with it.  When format contains non-ascii
339           characters it prints funny or gets "wide character warnings".  To
340           understand it, try the code below.
341
342             # Save this one in utf8
343             # replace *non-ascii* with a non-ascii string
344             my $camel;
345             format STDOUT =
346             *non-ascii*@>>>>>>>
347             $camel
348             .
349             $camel = "*non-ascii*";
350             binmode(STDOUT=>':encoding(utf8)'); # bang!
351             write;              # funny
352             print $camel, "\n"; # fine
353
354           Without binmode this happens to work but without binmode, print()
355           fails instead of write().
356
357           At any rate, the very use of format is questionable when it comes
358           to unicode characters since you have to consider such things as
359           character width (i.e. double-width for ideographs) and directions
360           (i.e. BIDI for Arabic and Hebrew).
361
362       Thread safety
363           "use encoding ..." is not thread-safe (i.e., do not use in threaded
364           applications).
365
366   The Logic of :locale
367       The logic of ":locale" is as follows:
368
369       1.  If the platform supports the langinfo(CODESET) interface, the
370           codeset returned is used as the default encoding for the open
371           pragma.
372
373       2.  If 1. didn't work but we are under the locale pragma, the
374           environment variables LC_ALL and LANG (in that order) are matched
375           for encodings (the part after ".", if any), and if any found, that
376           is used as the default encoding for the open pragma.
377
378       3.  If 1. and 2. didn't work, the environment variables LC_ALL and LANG
379           (in that order) are matched for anything looking like UTF-8, and if
380           any found, ":utf8" is used as the default encoding for the open
381           pragma.
382
383       If your locale environment variables (LC_ALL, LC_CTYPE, LANG) contain
384       the strings 'UTF-8' or 'UTF8' (case-insensitive matching), the default
385       encoding of your STDIN, STDOUT, and STDERR, and of any subsequent file
386       open, is UTF-8.
387

HISTORY

389       This pragma first appeared in Perl 5.8.0.  For features that require
390       5.8.1 and better, see above.
391
392       The ":locale" subpragma was implemented in 2.01, or Perl 5.8.6.
393