1utf8(3pm) Perl Programmers Reference Guide utf8(3pm)
2
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 # Convert a code point from the platform native character set to
25 # Unicode, and vice-versa.
26 $unicode = utf8::native_to_unicode(ord('A')); # returns 65 on both
27 # ASCII and EBCDIC
28 # platforms
29 $native = utf8::unicode_to_native(65); # returns 65 on ASCII
30 # platforms; 193 on
31 # EBCDIC
32 $flag = utf8::is_utf8($string); # since Perl 5.8.1
34 $flag = utf8::valid($string);
35
37 The "use utf8" pragma tells the Perl parser to allow UTF-8 in the
38 program text in the current lexical scope. The "no utf8" pragma tells
39 Perl to switch back to treating the source text as literal bytes in the
40 current lexical scope. (On EBCDIC platforms, technically it is
41 allowing UTF-EBCDIC, and not UTF-8, but this distinction is academic,
42 so in this document the term UTF-8 is used to mean both).
43 Do not use this pragma for anything else than telling Perl that your
45 script is written in UTF-8. The utility functions described below are
46 directly usable without "use utf8;".
47 Because it is not possible to reliably tell UTF-8 from native 8 bit
49 encodings, you need either a Byte Order Mark at the beginning of your
50 source code, or "use utf8;", to instruct perl.
51 When UTF-8 becomes the standard source format, this pragma will
53 effectively become a no-op.
54 See also the effects of the "-C" switch and its cousin, the
56 "PERL_UNICODE" environment variable, in perlrun.
57 Enabling the "utf8" pragma has the following effect:
59 • Bytes in the source text that are not in the ASCII character set
61 will be treated as being part of a literal UTF-8 sequence. This
62 includes most literals such as identifier names, string constants,
63 and constant regular expression patterns.
64 Note that if you have non-ASCII, non-UTF-8 bytes in your script (for
66 example embedded Latin-1 in your string literals), "use utf8" will be
67 unhappy. If you want to have such bytes under "use utf8", you can
68 disable this pragma until the end the block (or file, if at top level)
69 by "no utf8;".
70 Utility functions
72 The following functions are defined in the "utf8::" package by the Perl
73 core. You do not need to say "use utf8" to use these and in fact you
74 should not say that unless you really want to have UTF-8 source code.
75 • "$num_octets = utf8::upgrade($string)"
77 (Since Perl v5.8.0) Converts in-place the internal representation
79 of the string from an octet sequence in the native encoding
80 (Latin-1 or EBCDIC) to UTF-8. The logical character sequence itself
81 is unchanged. If $string is already upgraded, then this is a no-
82 op. Returns the number of octets necessary to represent the string
83 as UTF-8. Since Perl v5.38, if $string is "undef" no action is
84 taken; prior to that, it would be converted to be defined and zero-
85 length.
86 If your code needs to be compatible with versions of perl without
88 "use feature 'unicode_strings';", you can force Unicode semantics
89 on a given string:
90 # force unicode semantics for $string without the
92 # "unicode_strings" feature
93 utf8::upgrade($string);
94 For example:
96 # without explicit or implicit use feature 'unicode_strings'
98 my $x = "\xDF"; # LATIN SMALL LETTER SHARP S
99 $x =~ /ss/i; # won't match
100 my $y = uc($x); # won't convert
101 utf8::upgrade($x);
102 $x =~ /ss/i; # matches
103 my $z = uc($x); # converts to "SS"
104 Note that this function does not handle arbitrary encodings; use
106 Encode instead.
107 • "$success = utf8::downgrade($string[, $fail_ok])"
109 (Since Perl v5.8.0) Converts in-place the internal representation
111 of the string from UTF-8 to the equivalent octet sequence in the
112 native encoding (Latin-1 or EBCDIC). The logical character sequence
113 itself is unchanged. If $string is already stored as native 8 bit,
114 then this is a no-op. Can be used to make sure that the UTF-8 flag
115 is off, e.g. when you want to make sure that the substr() or
116 length() function works with the usually faster byte algorithm.
117 Fails if the original UTF-8 sequence cannot be represented in the
119 native 8 bit encoding. On failure dies or, if the value of $fail_ok
120 is true, returns false.
121 Returns true on success.
123 If your code expects an octet sequence this can be used to validate
125 that you've received one:
126 # throw an exception if not representable as octets
128 utf8::downgrade($string)
129 # or do your own error handling
131 utf8::downgrade($string, 1) or die "string must be octets";
132 Note that this function does not handle arbitrary encodings; use
134 Encode instead.
135 • utf8::encode($string)
137 (Since Perl v5.8.0) Converts in-place the character sequence to the
139 corresponding octet sequence in Perl's extended UTF-8. That is,
140 every (possibly wide) character gets replaced with a sequence of
141 one or more characters that represent the individual UTF-8 bytes of
142 the character. The UTF8 flag is turned off. Returns nothing.
143 my $x = "\x{100}"; # $x contains one character, with ord 0x100
145 utf8::encode($x); # $x contains two characters, with ords (on
146 # ASCII platforms) 0xc4 and 0x80. On EBCDIC
147 # 1047, this would instead be 0x8C and 0x41.
148 Similar to:
150 use Encode;
152 $x = Encode::encode("utf8", $x);
153 Note that this function does not handle arbitrary encodings; use
155 Encode instead.
156 • "$success = utf8::decode($string)"
158 (Since Perl v5.8.0) Attempts to convert in-place the octet sequence
160 encoded in Perl's extended UTF-8 to the corresponding character
161 sequence. That is, it replaces each sequence of characters in the
162 string whose ords represent a valid (extended) UTF-8 byte sequence,
163 with the corresponding single character. The UTF-8 flag is turned
164 on only if the source string contains multiple-byte UTF-8
165 characters. If $string is invalid as extended UTF-8, returns
166 false; otherwise returns true.
167 my $x = "\xc4\x80"; # $x contains two characters, with ords
169 # 0xc4 and 0x80
170 utf8::decode($x); # On ASCII platforms, $x contains one char,
171 # with ord 0x100. Since these bytes aren't
172 # legal UTF-EBCDIC, on EBCDIC platforms, $x is
173 # unchanged and the function returns FALSE.
174 my $y = "\xc3\x83\xc2\xab"; This has been encoded twice; this
175 # example is only for ASCII platforms
176 utf8::decode($y); # Converts $y to \xc3\xab, returns TRUE;
177 utf8::decode($y); # Further converts to \xeb, returns TRUE;
178 utf8::decode($y); # Returns FALSE, leaves $y unchanged
179 Note that this function does not handle arbitrary encodings; use
181 Encode instead.
182 • "$unicode = utf8::native_to_unicode($code_point)"
184 (Since Perl v5.8.0) This takes an unsigned integer (which
186 represents the ordinal number of a character (or a code point) on
187 the platform the program is being run on) and returns its Unicode
188 equivalent value. Since ASCII platforms natively use the Unicode
189 code points, this function returns its input on them. On EBCDIC
190 platforms it converts from EBCDIC to Unicode.
191 A meaningless value will currently be returned if the input is not
193 an unsigned integer.
194 Since Perl v5.22.0, calls to this function are optimized out on
196 ASCII platforms, so there is no performance hit in using it there.
197 • "$native = utf8::unicode_to_native($code_point)"
199 (Since Perl v5.8.0) This is the inverse of
201 utf8::native_to_unicode(), converting the other direction. Again,
202 on ASCII platforms, this returns its input, but on EBCDIC platforms
203 it will find the native platform code point, given any Unicode one.
204 A meaningless value will currently be returned if the input is not
206 an unsigned integer.
207 Since Perl v5.22.0, calls to this function are optimized out on
209 ASCII platforms, so there is no performance hit in using it there.
210 • "$flag = utf8::is_utf8($string)"
212 (Since Perl 5.8.1) Test whether $string is marked internally as
214 encoded in UTF-8. Functionally the same as
215 Encode::is_utf8($string).
216 Typically only necessary for debugging and testing, if you need to
218 dump the internals of an SV, Devel::Peek's Dump() provides more
219 detail in a compact form.
220 If you still think you need this outside of debugging, testing or
222 dealing with filenames, you should probably read perlunitut and
223 "What is "the UTF8 flag"?" in perlunifaq.
224 Don't use this flag as a marker to distinguish character and binary
226 data: that should be decided for each variable when you write your
227 code.
228 To force unicode semantics in code portable to perl 5.8 and 5.10,
230 call utf8::upgrade($string) unconditionally.
231 • "$flag = utf8::valid($string)"
233 [INTERNAL] Test whether $string is in a consistent state regarding
235 UTF-8. Will return true if it is well-formed Perl extended UTF-8
236 and has the UTF-8 flag on or if $string is held as bytes (both
237 these states are 'consistent'). The main reason for this routine
238 is to allow Perl's test suite to check that operations have left
239 strings in a consistent state.
240 "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.
242 See perlunicode, and the C API functions "sv_utf8_upgrade",
243 ""sv_utf8_downgrade" in perlapi", ""sv_utf8_encode" in perlapi", and
244 ""sv_utf8_decode" in perlapi", which are wrapped by the Perl functions
245 "utf8::upgrade", "utf8::downgrade", "utf8::encode" and "utf8::decode".
246 Also, the functions "utf8::is_utf8", "utf8::valid", "utf8::encode",
247 "utf8::decode", "utf8::upgrade", and "utf8::downgrade" are actually
248 internal, and thus always available, without a "require utf8"
249 statement.
250
252 Some filesystems may not support UTF-8 file names, or they may be
253 supported incompatibly with Perl. Therefore UTF-8 names that are
254 visible to the filesystem, such as module names may not work.
255
257 perlunitut, perluniintro, perlrun, bytes, perlunicode
258perl v5.38.2 2023-11-30 utf8(3pm)