1utf8(3pm)              Perl Programmers Reference Guide              utf8(3pm)
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3
4

NAME

6       utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source
7       code
8

SYNOPSIS

10        use utf8;
11        no utf8;
12
13        # Convert the internal representation of a Perl scalar to/from UTF-8.
14
15        $num_octets = utf8::upgrade($string);
16        $success    = utf8::downgrade($string[, $fail_ok]);
17
18        # Change each character of a Perl scalar to/from a series of
19        # characters that represent the UTF-8 bytes of each original character.
20
21        utf8::encode($string);  # "\x{100}"  becomes "\xc4\x80"
22        utf8::decode($string);  # "\xc4\x80" becomes "\x{100}"
23
24        # 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
33        $flag = utf8::is_utf8($string); # since Perl 5.8.1
34        $flag = utf8::valid($string);
35

DESCRIPTION

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
44       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
48       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
52       When UTF-8 becomes the standard source format, this pragma will
53       effectively become a no-op.
54
55       See also the effects of the "-C" switch and its cousin, the
56       "PERL_UNICODE" environment variable, in perlrun.
57
58       Enabling the "utf8" pragma has the following effect:
59
60       •   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
65       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
71   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
76       •   "$num_octets = utf8::upgrade($string)"
77
78           (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.
84
85           If your code needs to be compatible with versions of perl without
86           "use feature 'unicode_strings';", you can force Unicode semantics
87           on a given string:
88
89             # force unicode semantics for $string without the
90             # "unicode_strings" feature
91             utf8::upgrade($string);
92
93           For example:
94
95             # without explicit or implicit use feature 'unicode_strings'
96             my $x = "\xDF";    # LATIN SMALL LETTER SHARP S
97             $x =~ /ss/i;       # won't match
98             my $y = uc($x);    # won't convert
99             utf8::upgrade($x);
100             $x =~ /ss/i;       # matches
101             my $z = uc($x);    # converts to "SS"
102
103           Note that this function does not handle arbitrary encodings; use
104           Encode instead.
105
106       •   "$success = utf8::downgrade($string[, $fail_ok])"
107
108           (Since Perl v5.8.0) Converts in-place the internal representation
109           of the string from UTF-8 to the equivalent octet sequence in the
110           native encoding (Latin-1 or EBCDIC). The logical character sequence
111           itself is unchanged. If $string is already stored as native 8 bit,
112           then this is a no-op.  Can be used to make sure that the UTF-8 flag
113           is off, e.g. when you want to make sure that the substr() or
114           length() function works with the usually faster byte algorithm.
115
116           Fails if the original UTF-8 sequence cannot be represented in the
117           native 8 bit encoding. On failure dies or, if the value of $fail_ok
118           is true, returns false.
119
120           Returns true on success.
121
122           If your code expects an octet sequence this can be used to validate
123           that you've received one:
124
125             # throw an exception if not representable as octets
126             utf8::downgrade($string)
127
128             # or do your own error handling
129             utf8::downgrade($string, 1) or die "string must be octets";
130
131           Note that this function does not handle arbitrary encodings; use
132           Encode instead.
133
134       •   "utf8::encode($string)"
135
136           (Since Perl v5.8.0) Converts in-place the character sequence to the
137           corresponding octet sequence in Perl's extended UTF-8. That is,
138           every (possibly wide) character gets replaced with a sequence of
139           one or more characters that represent the individual UTF-8 bytes of
140           the character.  The UTF8 flag is turned off.  Returns nothing.
141
142            my $x = "\x{100}"; # $x contains one character, with ord 0x100
143            utf8::encode($x);  # $x contains two characters, with ords (on
144                               # ASCII platforms) 0xc4 and 0x80.  On EBCDIC
145                               # 1047, this would instead be 0x8C and 0x41.
146
147           Similar to:
148
149             use Encode;
150             $x = Encode::encode("utf8", $x);
151
152           Note that this function does not handle arbitrary encodings; use
153           Encode instead.
154
155       •   "$success = utf8::decode($string)"
156
157           (Since Perl v5.8.0) Attempts to convert in-place the octet sequence
158           encoded in Perl's extended UTF-8 to the corresponding character
159           sequence. That is, it replaces each sequence of characters in the
160           string whose ords represent a valid (extended) UTF-8 byte sequence,
161           with the corresponding single character.  The UTF-8 flag is turned
162           on only if the source string contains multiple-byte UTF-8
163           characters.  If $string is invalid as extended UTF-8, returns
164           false; otherwise returns true.
165
166            my $x = "\xc4\x80"; # $x contains two characters, with ords
167                                # 0xc4 and 0x80
168            utf8::decode($x);   # On ASCII platforms, $x contains one char,
169                                # with ord 0x100.   Since these bytes aren't
170                                # legal UTF-EBCDIC, on EBCDIC platforms, $x is
171                                # unchanged and the function returns FALSE.
172            my $y = "\xc3\x83\xc2\xab"; This has been encoded twice; this
173                                # example is only for ASCII platforms
174            utf8::decode($y);   # Converts $y to \xc3\xab, returns TRUE;
175            utf8::decode($y);   # Further converts to \xeb, returns TRUE;
176            utf8::decode($y);   # Returns FALSE, leaves $y unchanged
177
178           Note that this function does not handle arbitrary encodings; use
179           Encode instead.
180
181       •   "$unicode = utf8::native_to_unicode($code_point)"
182
183           (Since Perl v5.8.0) This takes an unsigned integer (which
184           represents the ordinal number of a character (or a code point) on
185           the platform the program is being run on) and returns its Unicode
186           equivalent value.  Since ASCII platforms natively use the Unicode
187           code points, this function returns its input on them.  On EBCDIC
188           platforms it converts from EBCDIC to Unicode.
189
190           A meaningless value will currently be returned if the input is not
191           an unsigned integer.
192
193           Since Perl v5.22.0, calls to this function are optimized out on
194           ASCII platforms, so there is no performance hit in using it there.
195
196       •   "$native = utf8::unicode_to_native($code_point)"
197
198           (Since Perl v5.8.0) This is the inverse of
199           "utf8::native_to_unicode()", converting the other direction.
200           Again, on ASCII platforms, this returns its input, but on EBCDIC
201           platforms it will find the native platform code point, given any
202           Unicode one.
203
204           A meaningless value will currently be returned if the input is not
205           an unsigned integer.
206
207           Since Perl v5.22.0, calls to this function are optimized out on
208           ASCII platforms, so there is no performance hit in using it there.
209
210       •   "$flag = utf8::is_utf8($string)"
211
212           (Since Perl 5.8.1)  Test whether $string is marked internally as
213           encoded in UTF-8.  Functionally the same as
214           "Encode::is_utf8($string)".
215
216           Typically only necessary for debugging and testing, if you need to
217           dump the internals of an SV, Devel::Peek's Dump() provides more
218           detail in a compact form.
219
220           If you still think you need this outside of debugging, testing or
221           dealing with filenames, you should probably read perlunitut and
222           "What is "the UTF8 flag"?" in perlunifaq.
223
224           Don't use this flag as a marker to distinguish character and binary
225           data: that should be decided for each variable when you write your
226           code.
227
228           To force unicode semantics in code portable to perl 5.8 and 5.10,
229           call "utf8::upgrade($string)" unconditionally.
230
231       •   "$flag = utf8::valid($string)"
232
233           [INTERNAL] Test whether $string is in a consistent state regarding
234           UTF-8.  Will return true if it is well-formed Perl extended UTF-8
235           and has the UTF-8 flag on or if $string is held as bytes (both
236           these states are 'consistent').  The main reason for this routine
237           is to allow Perl's test suite to check that operations have left
238           strings in a consistent state.
239
240       "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.
241       See perlunicode, and the C API functions "sv_utf8_upgrade",
242       ""sv_utf8_downgrade" in perlapi", ""sv_utf8_encode" in perlapi", and
243       ""sv_utf8_decode" in perlapi", which are wrapped by the Perl functions
244       "utf8::upgrade", "utf8::downgrade", "utf8::encode" and "utf8::decode".
245       Also, the functions "utf8::is_utf8", "utf8::valid", "utf8::encode",
246       "utf8::decode", "utf8::upgrade", and "utf8::downgrade" are actually
247       internal, and thus always available, without a "require utf8"
248       statement.
249

BUGS

251       Some filesystems may not support UTF-8 file names, or they may be
252       supported incompatibly with Perl.  Therefore UTF-8 names that are
253       visible to the filesystem, such as module names may not work.
254

SEE ALSO

256       perlunitut, perluniintro, perlrun, bytes, perlunicode
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259
260perl v5.36.0                      2022-08-30                         utf8(3pm)
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