utf8(3pm) Perl Programmers Reference Guide utf8(3pm)
utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
The "use utf8" pragma tells the Perl parser to allow UTF-8 in the program text in the cur-
rent 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 lex-
This pragma is primarily a compatibility device. Perl versions earlier than 5.6 allowed
arbitrary bytes in source code, whereas in future we would like to standardize on the
UTF-8 encoding for source text. Until UTF-8 becomes the default format for source text,
this pragma should be used to recognize UTF-8 in the source. When UTF-8 becomes the stan-
dard 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.
Enabling the "utf8" pragma has the following effect:
o Bytes in the source text that have their high-bit set will be treated as being part of
a literal UTF-8 character. 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-8. If you want to have such bytes and use utf8, you can dis-
able utf8 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.
o $num_octets = utf8::upgrade($string);
Converts (in-place) internal representation of string to Perl's internal UTF-X form.
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 expected on
strings containing characters in the range 0x80-0xFF. Note that this should not be
used to convert a legacy byte encoding to Unicode: use Encode for that. Affected by
the encoding pragma.
o utf8::downgrade($string[, FAIL_OK])
Converts (in-place) internal representation of string to be un-encoded bytes. Returns
true on success. On failure dies or, if the value of FAIL_OK is true, returns false.
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.
Note that this should not be used to convert Unicode back to a legacy byte encoding:
use Encode for that. Not affected by the encoding pragma.
Converts (in-place) $string from logical characters to octet sequence representing it
in Perl's UTF-X encoding. Same as Encode::encode_utf8(). Note that this should not be
used to convert a legacy byte encoding to Unicode: use Encode for that.
o $flag = utf8::decode($string)
Attempts to convert $string in-place from Perl's UTF-X encoding into logical charac-
ters. Same as Encode::decode_utf8(). Note that this should not be used to convert Uni-
code back to a legacy byte encoding: use Encode for that.
o $flag = utf8::valid(STRING)
[INTERNAL] Test whether STRING is in a consistent state. Will return true if string
is held as bytes, or is well-formed UTF-8 and has the UTF-8 flag on. Main reason for
this routine is to allow Perl's testsuite 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 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". Note that in the
Perl 5.8.0 implementation the functions utf8::valid, utf8::encode, utf8::decode,
utf8::upgrade, and utf8::downgrade are always available, without a "require utf8" state-
ment-- this may change in future releases.
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
perl v5.8.0 2002-06-01 utf8(3pm)