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 a Perl scalar to/from UTF-8.
14 $num_octets = utf8::upgrade($string);
15 $success = utf8::downgrade($string[, FAIL_OK]);
16 # Change the native bytes of a Perl scalar to/from UTF-8 bytes.
18 utf8::encode($string);
19 utf8::decode($string);
20 $flag = utf8::is_utf8(STRING); # since Perl 5.8.1
22 $flag = utf8::valid(STRING);
23
25 The "use utf8" pragma tells the Perl parser to allow UTF-8 in the pro‐
26 gram text in the current lexical scope (allow UTF-EBCDIC on EBCDIC
27 based platforms). The "no utf8" pragma tells Perl to switch back to
28 treating the source text as literal bytes in the current lexical scope.
29 This pragma is primarily a compatibility device. Perl versions earlier
31 than 5.6 allowed arbitrary bytes in source code, whereas in future we
32 would like to standardize on the UTF-8 encoding for source text.
33 Do not use this pragma for anything else than telling Perl that your
35 script is written in UTF-8. The utility functions described below are
36 useful for their own purposes, but they are not really part of the
37 "pragmatic" effect.
38 Until UTF-8 becomes the default format for source text, either this
40 pragma or the encoding pragma should be used to recognize UTF-8 in the
41 source. When UTF-8 becomes the standard source format, this pragma
42 will effectively become a no-op. For convenience in what follows the
43 term UTF-X is used to refer to UTF-8 on ASCII and ISO Latin based plat‐
44 forms 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-8 character. This includes
53 most literals such as identifier names, string constants, and con‐
54 stant 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-8. If
62 you want to have such bytes and use utf8, you can disable utf8 until
63 the end the block (or file, if at top level) by "no utf8;".
64 If you want to automatically upgrade your 8-bit legacy bytes to UTF-8,
66 use the encoding pragma instead of this pragma. For example, if you
67 want to implicitly upgrade your ISO 8859-1 (Latin-1) bytes to UTF-8 as
68 used in e.g. "chr()" and "\x{...}", try this:
69 use encoding "latin-1";
71 my $c = chr(0xc4);
72 my $x = "\x{c5}";
73 In case you are wondering: yes, "use encoding 'utf8';" works much the
75 same as "use utf8;".
76 Utility functions
78 The following functions are defined in the "utf8::" package by the Perl
80 core. You do not need to say "use utf8" to use these and in fact you
81 should not say that unless you really want to have UTF-8 source code.
82 * $num_octets = utf8::upgrade($string)
84 Converts in-place the octet sequence in the native encoding
85 (Latin-1 or EBCDIC) to the equivalent character sequence in UTF-X.
86 $string already encoded as characters does no harm. Returns the
87 number of octets necessary to represent the string as UTF-X. Can
88 be used to make sure that the UTF-8 flag is on, so that "\w" or
89 "lc()" work as Unicode on strings containing characters in the
90 range 0x80-0xFF (on ASCII and derivatives).
91 Note that this function does not handle arbitrary encodings.
93 Therefore Encode.pm is recommended for the general purposes.
94 Affected by the encoding pragma.
96 * $success = utf8::downgrade($string[, FAIL_OK])
98 Converts in-place the character sequence in UTF-X to the equivalent
99 octet sequence in the native encoding (Latin-1 or EBCDIC). $string
100 already encoded as octets does no harm. Returns true on success.
101 On failure dies or, if the value of "FAIL_OK" is true, returns
102 false. Can be used to make sure that the UTF-8 flag is off, e.g.
103 when you want to make sure that the substr() or length() function
104 works with the usually faster byte algorithm.
105 Note that this function does not handle arbitrary encodings.
107 Therefore Encode.pm is recommended for the general purposes.
108 Not affected by the encoding pragma.
110 NOTE: this function is experimental and may change or be removed
112 without notice.
113 * utf8::encode($string)
115 Converts in-place the character sequence to the corresponding octet
116 sequence in UTF-X. The UTF-8 flag is turned off. Returns nothing.
117 Note that this function does not handle arbitrary encodings.
119 Therefore Encode.pm is recommended for the general purposes.
120 * utf8::decode($string)
122 Attempts to convert in-place the octet sequence in UTF-X to the
123 corresponding character sequence. The UTF-8 flag is turned on only
124 if the source string contains multiple-byte UTF-X characters. If
125 $string is invalid as UTF-X, returns false; otherwise returns true.
126 Note that this function does not handle arbitrary encodings.
128 Therefore Encode.pm is recommended for the general purposes.
129 NOTE: this function is experimental and may change or be removed
131 without notice.
132 * $flag = utf8::is_utf8(STRING)
134 (Since Perl 5.8.1) Test whether STRING is in UTF-8. Functionally
135 the same as Encode::is_utf8().
136 * $flag = utf8::valid(STRING)
138 [INTERNAL] Test whether STRING is in a consistent state regarding
139 UTF-8. Will return true is well-formed UTF-8 and has the UTF-8
140 flag on or if string is held as bytes (both these states are 'con‐
141 sistent'). Main reason for this routine is to allow Perl's test‐
142 suite to check that operations have left strings in a consistent
143 state. You most probably want to use utf8::is_utf8() instead.
144 "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.
146 See perlunicode for more on the UTF8 flag and the C API functions
147 "sv_utf8_upgrade", "sv_utf8_downgrade", "sv_utf8_encode", and
148 "sv_utf8_decode", which are wrapped by the Perl functions
149 "utf8::upgrade", "utf8::downgrade", "utf8::encode" and "utf8::decode".
150 Note that in the Perl 5.8.0 and 5.8.1 implementation the functions
151 utf8::is_utf8, utf8::valid, utf8::encode, utf8::decode, utf8::upgrade,
152 and utf8::downgrade are always available, without a "require utf8"
153 statement-- this may change in future releases.
154
156 One can have Unicode in identifier names, but not in package/class or
157 subroutine names. While some limited functionality towards this does
158 exist as of Perl 5.8.0, that is more accidental than designed; use of
159 Unicode for the said purposes is unsupported.
160 One reason of this unfinishedness is its (currently) inherent unporta‐
162 bility: since both package names and subroutine names may need to be
163 mapped to file and directory names, the Unicode capability of the
164 filesystem becomes important-- and there unfortunately aren't portable
165 answers.
166
168 perluniintro, encoding, perlrun, bytes, perlunicode
169perl v5.8.8 2001-09-21 utf8(3pm)