1utf8(3pm) Perl Programmers Reference Guide utf8(3pm)
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6 utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source
7 code
8
10 use utf8;
11 no utf8;
12 # Convert the internal representation of a Perl scalar to/from UTF-8.
14 $num_octets = utf8::upgrade($string);
16 $success = utf8::downgrade($string[, FAIL_OK]);
17 # Change each character of a Perl scalar to/from a series of
19 # characters that represent the UTF-8 bytes of each original character.
20 utf8::encode($string); # "\x{100}" becomes "\xc4\x80"
22 utf8::decode($string); # "\xc4\x80" becomes "\x{100}"
23 $flag = utf8::is_utf8(STRING); # since Perl 5.8.1
25 $flag = utf8::valid(STRING);
26
28 The "use utf8" pragma tells the Perl parser to allow UTF-8 in the
29 program text in the current lexical scope (allow UTF-EBCDIC on EBCDIC
30 based platforms). The "no utf8" pragma tells Perl to switch back to
31 treating the source text as literal bytes in the current lexical scope.
32 Do not use this pragma for anything else than telling Perl that your
34 script is written in UTF-8. The utility functions described below are
35 directly usable without "use utf8;".
36 Because it is not possible to reliably tell UTF-8 from native 8 bit
38 encodings, you need either a Byte Order Mark at the beginning of your
39 source code, or "use utf8;", to instruct perl.
40 When UTF-8 becomes the standard source format, this pragma will
42 effectively become a no-op. For convenience in what follows the term
43 UTF-X is used to refer to UTF-8 on ASCII and ISO Latin based platforms
44 and UTF-EBCDIC on EBCDIC based platforms.
45 See also the effects of the "-C" switch and its cousin, the
47 $ENV{PERL_UNICODE}, in perlrun.
48 Enabling the "utf8" pragma has the following effect:
50 · Bytes in the source text that have their high-bit set will be
52 treated as being part of a literal UTF-X sequence. This includes
53 most literals such as identifier names, string constants, and
54 constant regular expression patterns.
55 On EBCDIC platforms characters in the Latin 1 character set are
57 treated as being part of a literal UTF-EBCDIC character.
58 Note that if you have bytes with the eighth bit on in your script (for
60 example embedded Latin-1 in your string literals), "use utf8" will be
61 unhappy since the bytes are most probably not well-formed UTF-X. If
62 you want to have such bytes under "use utf8", you can disable this
63 pragma until the end the block (or file, if at top level) by "no
64 utf8;".
65 Utility functions
67 The following functions are defined in the "utf8::" package by the Perl
68 core. You do not need to say "use utf8" to use these and in fact you
69 should not say that unless you really want to have UTF-8 source code.
70 · $num_octets = utf8::upgrade($string)
72 Converts in-place the internal representation of the string from an
74 octet sequence in the native encoding (Latin-1 or EBCDIC) to UTF-X.
75 The logical character sequence itself is unchanged. If $string is
76 already stored as UTF-X, then this is a no-op. Returns the number
77 of octets necessary to represent the string as UTF-X. Can be used
78 to make sure that the UTF-8 flag is on, so that "\w" or "lc()" work
79 as Unicode on strings containing characters in the range 0x80-0xFF
80 (on ASCII and derivatives).
81 Note that this function does not handle arbitrary encodings.
83 Therefore Encode is recommended for the general purposes; see also
84 Encode.
85 · $success = utf8::downgrade($string[, FAIL_OK])
87 Converts in-place the internal representation of the string from
89 UTF-X to the equivalent octet sequence in the native encoding
90 (Latin-1 or EBCDIC). The logical character sequence itself is
91 unchanged. If $string is already stored as native 8 bit, then this
92 is a no-op. Can be used to make sure that the UTF-8 flag is off,
93 e.g. when you want to make sure that the substr() or length()
94 function works with the usually faster byte algorithm.
95 Fails if the original UTF-X sequence cannot be represented in the
97 native 8 bit encoding. On failure dies or, if the value of
98 "FAIL_OK" is true, returns false.
99 Returns true on success.
101 Note that this function does not handle arbitrary encodings.
103 Therefore Encode is recommended for the general purposes; see also
104 Encode.
105 · utf8::encode($string)
107 Converts in-place the character sequence to the corresponding octet
109 sequence in UTF-X. That is, every (possibly wide) character gets
110 replaced with a sequence of one or more characters that represent
111 the individual UTF-X bytes of the character. The UTF8 flag is
112 turned off. Returns nothing.
113 my $a = "\x{100}"; # $a contains one character, with ord 0x100
115 utf8::encode($a); # $a contains two characters, with ords 0xc4 and 0x80
116 Note that this function does not handle arbitrary encodings.
118 Therefore Encode is recommended for the general purposes; see also
119 Encode.
120 · $success = utf8::decode($string)
122 Attempts to convert in-place the octet sequence in UTF-X to the
124 corresponding character sequence. That is, it replaces each
125 sequence of characters in the string whose ords represent a valid
126 UTF-X byte sequence, with the corresponding single character. The
127 UTF-8 flag is turned on only if the source string contains
128 multiple-byte UTF-X characters. If $string is invalid as UTF-X,
129 returns false; otherwise returns true.
130 my $a = "\xc4\x80"; # $a contains two characters, with ords 0xc4 and 0x80
132 utf8::decode($a); # $a contains one character, with ord 0x100
133 Note that this function does not handle arbitrary encodings.
135 Therefore Encode is recommended for the general purposes; see also
136 Encode.
137 · $flag = utf8::is_utf8(STRING)
139 (Since Perl 5.8.1) Test whether STRING is in UTF-8 internally.
141 Functionally the same as Encode::is_utf8().
142 · $flag = utf8::valid(STRING)
144 [INTERNAL] Test whether STRING is in a consistent state regarding
146 UTF-8. Will return true is well-formed UTF-8 and has the UTF-8
147 flag on or if string is held as bytes (both these states are
148 'consistent'). Main reason for this routine is to allow Perl's
149 testsuite to check that operations have left strings in a
150 consistent state. You most probably want to use utf8::is_utf8()
151 instead.
152 "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.
154 See perlunicode for more on the UTF8 flag and the C API functions
155 "sv_utf8_upgrade", "sv_utf8_downgrade", "sv_utf8_encode", and
156 "sv_utf8_decode", which are wrapped by the Perl functions
157 "utf8::upgrade", "utf8::downgrade", "utf8::encode" and "utf8::decode".
158 Also, the functions utf8::is_utf8, utf8::valid, utf8::encode,
159 utf8::decode, utf8::upgrade, and utf8::downgrade are actually internal,
160 and thus always available, without a "require utf8" statement.
161
163 One can have Unicode in identifier names, but not in package/class or
164 subroutine names. While some limited functionality towards this does
165 exist as of Perl 5.8.0, that is more accidental than designed; use of
166 Unicode for the said purposes is unsupported.
167 One reason of this unfinishedness is its (currently) inherent
169 unportability: since both package names and subroutine names may need
170 to be mapped to file and directory names, the Unicode capability of the
171 filesystem becomes important-- and there unfortunately aren't portable
172 answers.
173
175 perlunitut, perluniintro, perlrun, bytes, perlunicode
176perl v5.16.3 2013-03-04 utf8(3pm)