utf8(3pm) Perl Programmers Reference Guide utf8(3pm)
NAME
utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source
code
SYNOPSIS
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);
DESCRIPTION
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:
o 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;".
Utility functions
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.
o "$num_octets = utf8::upgrade($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 $string is already stored as UTF-8, then this is
a no-op. Returns the number of octets necessary to represent the
string as UTF-8. Can be used to make sure that the UTF-8 flag is
on, so that "\w" or "lc()" work as Unicode on strings containing
non-ASCII characters whose code points are below 256.
Note that this function does not handle arbitrary encodings; use
Encode instead.
o "$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 $fail_ok
is true, returns false.
Returns true on success.
Note that this function does not handle arbitrary encodings; use
Encode instead.
o "utf8::encode($string)"
(Since Perl v5.8.0) Converts in-place the character sequence to the
corresponding octet sequence in 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 $a = "\x{100}"; # $a contains one character, with ord 0x100
utf8::encode($a); # $a contains two characters, with ords (on
# ASCII platforms) 0xc4 and 0x80. On EBCDIC
# 1047, this would instead be 0x8C and 0x41.
Note that this function does not handle arbitrary encodings; use
Encode instead.
o "$success = utf8::decode($string)"
(Since Perl v5.8.0) Attempts to convert in-place the octet sequence
encoded as UTF-8 to the corresponding character sequence. That is,
it replaces each sequence of characters in the string whose ords
represent a valid 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 UTF-8, returns false; otherwise returns true.
my $a = "\xc4\x80"; # $a contains two characters, with ords
# 0xc4 and 0x80
utf8::decode($a); # On ASCII platforms, $a contains one char,
# with ord 0x100. Since these bytes aren't
# legal UTF-EBCDIC, on EBCDIC platforms, $a is
# unchanged and the function returns FALSE.
Note that this function does not handle arbitrary encodings; use
Encode instead.
o "$unicode = utf8::native_to_unicode($code_point)"
(Since Perl v5.8.0) This takes an unsigned integer (which
represents the ordinal number of a character (or a code point) on
the platform the program is being run on) and returns its Unicode
equivalent value. Since ASCII platforms natively use the Unicode
code points, this function returns its input on them. On EBCDIC
platforms it converts from EBCDIC to Unicode.
A meaningless value will currently be returned if the input is not
an unsigned integer.
Since Perl v5.22.0, calls to this function are optimized out on
ASCII platforms, so there is no performance hit in using it there.
o "$native = utf8::unicode_to_native($code_point)"
(Since Perl v5.8.0) This is the inverse of
"utf8::native_to_unicode()", converting the other direction.
Again, on ASCII platforms, this returns its input, but on EBCDIC
platforms it will find the native platform code point, given any
Unicode one.
A meaningless value will currently be returned if the input is not
an unsigned integer.
Since Perl v5.22.0, calls to this function are optimized out on
ASCII platforms, so there is no performance hit in using it there.
o "$flag = utf8::is_utf8($string)"
(Since Perl 5.8.1) Test whether $string is marked internally as
encoded in UTF-8. Functionally the same as "Encode::is_utf8()".
o "$flag = utf8::valid($string)"
[INTERNAL] Test whether $string is in a consistent state regarding
UTF-8. Will return true if it is well-formed UTF-8 and has the
UTF-8 flag on or if $string is held as bytes (both these states are
'consistent'). Main reason for this routine is to allow Perl's
test suite to check that operations have left strings in a
consistent state. You most probably want to use "utf8::is_utf8()"
instead.
"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.
BUGS
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.
SEE ALSO
perlunitut, perluniintro, perlrun, bytes, perlunicode
perl v5.26.3 2018-03-01 utf8(3pm)
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