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utf8(3) |
Perl Programmers Reference Guide |
utf8(3) |
utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
use utf8;
no utf8;
# Convert the internal representation of a Perl scalar to/from UTF-8.
$num_octets = utf8::upgrade($string);
$success = utf8::downgrade($string[, $fail_ok]);
# Change each character of a Perl scalar to/from a series of
# characters that represent the UTF-8 bytes of each original character.
utf8::encode($string); # "\x{100}" becomes "\xc4\x80"
utf8::decode($string); # "\xc4\x80" becomes "\x{100}"
# Convert a code point from the platform native character set to
# Unicode, and vice-versa.
$unicode = utf8::native_to_unicode(ord('A')); # returns 65 on both
# ASCII and EBCDIC
# platforms
$native = utf8::unicode_to_native(65); # returns 65 on ASCII
# platforms; 193 on
# EBCDIC
$flag = utf8::is_utf8($string); # since Perl 5.8.1
$flag = utf8::valid($string);
The "use utf8" pragma tells the Perl parser to
allow UTF-8 in the program text in the current lexical scope. The
"no utf8" pragma tells Perl to switch back
to treating the source text as literal bytes in the current lexical scope. (On
EBCDIC platforms, technically it is allowing UTF-EBCDIC, and not UTF-8, but
this distinction is academic, so in this document the term UTF-8 is used to
mean both).
Do not use this pragma for anything else than telling Perl that
your script is written in UTF-8. The utility functions described
below are directly usable without "use
utf8;".
Because it is not possible to reliably tell UTF-8 from native 8
bit encodings, you need either a Byte Order Mark at the beginning of your
source code, or "use utf8;", to instruct
perl.
When UTF-8 becomes the standard source format, this pragma will
effectively become a no-op.
See also the effects of the "-C"
switch and its cousin, the "PERL_UNICODE"
environment variable, in perlrun.
Enabling the "utf8" pragma has
the following effect:
- •
- Bytes in the source text that are not in the ASCII character set will be
treated as being part of a literal UTF-8 sequence. This includes most
literals such as identifier names, string constants, and constant regular
expression patterns.
Note that if you have non-ASCII, non-UTF-8 bytes in your script
(for example embedded Latin-1 in your string literals),
"use utf8" will be unhappy. If you want to
have such bytes under "use utf8", you can
disable this pragma until the end the block (or file, if at top level) by
"no utf8;".
The following functions are defined in the
"utf8::" package by the Perl core. You do
not need to say "use utf8" to use these and
in fact you should not say that unless you really want to have UTF-8 source
code.
- "$num_octets = utf8::upgrade($string)"
(Since Perl v5.8.0) Converts in-place the internal
representation of the string from an octet sequence in the native
encoding (Latin-1 or EBCDIC) to UTF-8. The logical character sequence
itself is unchanged. If $string is already
upgraded, then this is a no-op. Returns the number of octets necessary
to represent the string as UTF-8.
If your code needs to be compatible with versions of perl
without "use feature
'unicode_strings';", you can force Unicode semantics on a
given string:
# force unicode semantics for $string without the
# "unicode_strings" feature
utf8::upgrade($string);
For example:
# without explicit or implicit use feature 'unicode_strings'
my $x = "\xDF"; # LATIN SMALL LETTER SHARP S
$x =~ /ss/i; # won't match
my $y = uc($x); # won't convert
utf8::upgrade($x);
$x =~ /ss/i; # matches
my $z = uc($x); # converts to "SS"
Note that this function does not handle arbitrary
encodings; use Encode instead.
- "$success = utf8::downgrade($string[,
$fail_ok])"
(Since Perl v5.8.0) Converts in-place the internal
representation of the string from UTF-8 to the equivalent octet sequence
in the native encoding (Latin-1 or EBCDIC). The logical character
sequence itself is unchanged. If $string is already
stored as native 8 bit, then this is a no-op. Can be used to make sure
that the UTF-8 flag is off, e.g. when you want to make sure that the
substr() or length() function works with the usually
faster byte algorithm.
Fails if the original UTF-8 sequence cannot be represented in
the native 8 bit encoding. On failure dies or, if the value of
$fail_ok is true, returns false.
Returns true on success.
If your code expects an octet sequence this can be used to
validate that you've received one:
# throw an exception if not representable as octets
utf8::downgrade($string)
# or do your own error handling
utf8::downgrade($string, 1) or die "string must be octets";
Note that this function does not handle arbitrary
encodings; use Encode instead.
- "utf8::encode($string)"
(Since Perl v5.8.0) Converts in-place the character sequence
to the corresponding octet sequence in Perl's extended UTF-8. That is,
every (possibly wide) character gets replaced with a sequence of one or
more characters that represent the individual UTF-8 bytes of the
character. The UTF8 flag is turned off. Returns nothing.
my $x = "\x{100}"; # $x contains one character, with ord 0x100
utf8::encode($x); # $x contains two characters, with ords (on
# ASCII platforms) 0xc4 and 0x80. On EBCDIC
# 1047, this would instead be 0x8C and 0x41.
Similar to:
use Encode;
$x = Encode::encode("utf8", $x);
Note that this function does not handle arbitrary
encodings; use Encode instead.
- "$success = utf8::decode($string)"
(Since Perl v5.8.0) Attempts to convert in-place the octet
sequence encoded in Perl's extended UTF-8 to the corresponding character
sequence. That is, it replaces each sequence of characters in the string
whose ords represent a valid (extended) UTF-8 byte sequence, with the
corresponding single character. The UTF-8 flag is turned on only if the
source string contains multiple-byte UTF-8 characters. If
$string is invalid as extended UTF-8, returns
false; otherwise returns true.
my $x = "\xc4\x80"; # $x contains two characters, with ords
# 0xc4 and 0x80
utf8::decode($x); # On ASCII platforms, $x contains one char,
# with ord 0x100. Since these bytes aren't
# legal UTF-EBCDIC, on EBCDIC platforms, $x is
# unchanged and the function returns FALSE.
my $y = "\xc3\x83\xc2\xab"; This has been encoded twice; this
# example is only for ASCII platforms
utf8::decode($y); # Converts $y to \xc3\xab, returns TRUE;
utf8::decode($y); # Further converts to \xeb, returns TRUE;
utf8::decode($y); # Returns FALSE, leaves $y unchanged
Note that this function does not handle arbitrary
encodings; use Encode instead.
- "$unicode =
utf8::native_to_unicode($code_point)"
(Since Perl v5.8.0) This takes an unsigned integer (which
represents the ordinal number of a character (or a code point) on the
platform the program is being run on) and returns its Unicode equivalent
value. Since ASCII platforms natively use the Unicode code points, this
function returns its input on them. On EBCDIC platforms it converts from
EBCDIC to Unicode.
A meaningless value will currently be returned if the input is
not an unsigned integer.
Since Perl v5.22.0, calls to this function are optimized out
on ASCII platforms, so there is no performance hit in using it
there.
- "$native =
utf8::unicode_to_native($code_point)"
(Since Perl v5.8.0) This is the inverse of
"utf8::native_to_unicode()",
converting the other direction. Again, on ASCII platforms, this returns
its input, but on EBCDIC platforms it will find the native platform code
point, given any Unicode one.
A meaningless value will currently be returned if the input is
not an unsigned integer.
Since Perl v5.22.0, calls to this function are optimized out
on ASCII platforms, so there is no performance hit in using it
there.
- "$flag = utf8::is_utf8($string)"
(Since Perl 5.8.1) Test whether $string
is marked internally as encoded in UTF-8. Functionally the same as
"Encode::is_utf8($string)".
Typically only necessary for debugging and testing, if you
need to dump the internals of an SV, Devel::Peek's Dump()
provides more detail in a compact form.
If you still think you need this outside of debugging, testing
or dealing with filenames, you should probably read perlunitut and
"What is "the UTF8 flag"?" in perlunifaq.
Don't use this flag as a marker to distinguish character and
binary data: that should be decided for each variable when you write
your code.
To force unicode semantics in code portable to perl 5.8 and
5.10, call "utf8::upgrade($string)"
unconditionally.
- "$flag = utf8::valid($string)"
[INTERNAL] Test whether $string is in a
consistent state regarding UTF-8. Will return true if it is well-formed
Perl extended UTF-8 and has the UTF-8 flag on or if
$string is held as bytes (both these states are
'consistent'). The main reason for this routine is to allow Perl's test
suite to check that operations have left strings in a consistent
state.
"utf8::encode" is like
"utf8::upgrade", but the UTF8 flag is
cleared. See perlunicode, and the C API functions
"sv_utf8_upgrade",
""sv_utf8_downgrade" in
perlapi", ""sv_utf8_encode" in
perlapi", and ""sv_utf8_decode"
in perlapi", which are wrapped by the Perl functions
"utf8::upgrade",
"utf8::downgrade",
"utf8::encode" and
"utf8::decode". Also, the functions
"utf8::is_utf8",
"utf8::valid",
"utf8::encode",
"utf8::decode",
"utf8::upgrade", and
"utf8::downgrade" are actually internal,
and thus always available, without a "require
utf8" statement.
Some filesystems may not support UTF-8 file names, or they may be supported
incompatibly with Perl. Therefore UTF-8 names that are visible to the
filesystem, such as module names may not work.
perlunitut, perluniintro, perlrun, bytes, perlunicode
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