Provided by: perl-doc_5.22.1-9ubuntu0.9_all 
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 (allow UTF-EBCDIC on EBCDIC based platforms). The "no utf8" pragma tells Perl to switch back to
treating the source text as literal bytes in the current lexical scope.
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. For
convenience in what follows the term UTF-X is used to refer to UTF-8 on ASCII and ISO Latin based
platforms and UTF-EBCDIC on EBCDIC based platforms.
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 have their high-bit set will be treated as being part of a literal UTF-
X sequence. This includes most literals such as identifier names, string constants, and constant
regular expression patterns.
On EBCDIC platforms characters in the Latin 1 character set are treated as being part of a literal
UTF-EBCDIC character.
Note that if you have bytes with the eighth bit on in your script (for example embedded Latin-1 in your
string literals), "use utf8" will be unhappy since the bytes are most probably not well-formed UTF-X. 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.
• "$num_octets = utf8::upgrade($string)"
Converts in-place the internal representation of the string from an octet sequence in the native
encoding (Latin-1 or EBCDIC) to UTF-X. The logical character sequence itself is unchanged. If
$string is already stored as UTF-X, then this is a no-op. Returns the number of octets necessary to
represent the string as UTF-X. Can be used to make sure that the UTF-8 flag is on, so that "\w" or
"lc()" work as Unicode on strings containing characters in the range 0x80-0xFF (on ASCII and
derivatives).
Note that this function does not handle arbitrary encodings. Therefore Encode is recommended for the
general purposes; see also Encode.
• "$success = utf8::downgrade($string[, $fail_ok])"
Converts in-place the internal representation of the string from UTF-X 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-X sequence cannot be represented in the native 8 bit encoding. On failure
dies or, if the value of $fail_ok is true, returns false.
Returns true on success.
Note that this function does not handle arbitrary encodings. Therefore Encode is recommended for the
general purposes; see also Encode.
• "utf8::encode($string)"
Converts in-place the character sequence to the corresponding octet sequence in UTF-X. That is, every
(possibly wide) character gets replaced with a sequence of one or more characters that represent the
individual UTF-X 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); # $a contains two characters, with ords (on
# ASCII platforms) 0xc4 and 0x80
Note that this function does not handle arbitrary encodings. Therefore Encode is recommended for the
general purposes; see also Encode.
• "$success = utf8::decode($string)"
Attempts to convert in-place the octet sequence encoded as UTF-X to the corresponding character
sequence. That is, it replaces each sequence of characters in the string whose ords represent a valid
UTF-X byte sequence, with the corresponding single character. The UTF-8 flag is turned on only if
the source string contains multiple-byte UTF-X characters. If $string is invalid as UTF-X, 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. On EBCDIC platforms, $a
# is unchanged and the function returns FALSE.
("\xc4\x80" is not a valid sequence of bytes in any UTF-8-encoded character(s) in the EBCDIC code
pages that Perl supports, which is why the above example returns failure on them. What does decode
into "\x{100}" depends on the platform. It is "\x8C\x41" in IBM-1047.)
Note that this function does not handle arbitrary encodings. Therefore Encode is recommended for the
general purposes; see also Encode.
• "$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 $string is marked internally as encoded in UTF-8. Functionally the
same as Encode::is_utf8().
• "$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 for more on the
UTF8 flag and the C API functions "sv_utf8_upgrade", "sv_utf8_downgrade", "sv_utf8_encode", and
"sv_utf8_decode", 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
One can have Unicode in identifier names, but not in package/class or subroutine names. While some
limited functionality towards this does exist as of Perl 5.8.0, that is more accidental than designed;
use of Unicode for the said purposes is unsupported.
One reason of this unfinishedness is its (currently) inherent unportability: since both package names and
subroutine names may need to be mapped to file and directory names, the Unicode capability of the
filesystem becomes important-- and there unfortunately aren't portable answers.
SEE ALSO
perlunitut, perluniintro, perlrun, bytes, perlunicode
perl v5.22.1 2020-10-19 utf8(3perl)