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bytes(3perl) Perl Programmers Reference Guide bytes(3perl) NAME
bytes - Perl pragma to force byte semantics rather than character semantics NOTICE
This pragma reflects early attempts to incorporate Unicode into perl and has since been superseded. It breaks encapsulation (i.e. it exposes the innards of how the perl executable currently happens to store a string), and use of this module for anything other than debugging purposes is strongly discouraged. If you feel that the functions here within might be useful for your application, this possibly indicates a mismatch between your mental model of Perl Unicode and the current reality. In that case, you may wish to read some of the perl Unicode documentation: perluniintro, perlunitut, perlunifaq and perlunicode. SYNOPSIS
use bytes; ... chr(...); # or bytes::chr ... index(...); # or bytes::index ... length(...); # or bytes::length ... ord(...); # or bytes::ord ... rindex(...); # or bytes::rindex ... substr(...); # or bytes::substr no bytes; DESCRIPTION
The "use bytes" pragma disables character semantics for the rest of the lexical scope in which it appears. "no bytes" can be used to reverse the effect of "use bytes" within the current lexical scope. Perl normally assumes character semantics in the presence of character data (i.e. data that has come from a source that has been marked as being of a particular character encoding). When "use bytes" is in effect, the encoding is temporarily ignored, and each string is treated as a series of bytes. As an example, when Perl sees "$x = chr(400)", it encodes the character in UTF-8 and stores it in $x. Then it is marked as character data, so, for instance, "length $x" returns 1. However, in the scope of the "bytes" pragma, $x is treated as a series of bytes - the bytes that make up the UTF8 encoding - and "length $x" returns 2: $x = chr(400); print "Length is ", length $x, " "; # "Length is 1" printf "Contents are %vd ", $x; # "Contents are 400" { use bytes; # or "require bytes; bytes::length()" print "Length is ", length $x, " "; # "Length is 2" printf "Contents are %vd ", $x; # "Contents are 198.144" } chr(), ord(), substr(), index() and rindex() behave similarly. For more on the implications and differences between character semantics and byte semantics, see perluniintro and perlunicode. LIMITATIONS
bytes::substr() does not work as an lvalue(). SEE ALSO
perluniintro, perlunicode, utf8 perl v5.14.2 2010-12-30 bytes(3perl)
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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; 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. 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 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. 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 disable utf8 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. 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 repre- sent 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 con- taining 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($string[, FAIL_OK]) Converts (in-place) internal representation of string to be un-encoded bytes. Returns true on success. On failure dies or, if the value of FAIL_OK is true, returns false. Can be used to make sure that the UTF-8 flag is off, e.g. when you want to make sure that the substr() or length() function works with the usually faster byte algorithm. Note that this should not be used to convert Unicode back to a legacy byte encoding: use Encode for that. Not affected by the encoding pragma. o utf8::encode($string) 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 characters. Same as Encode::decode_utf8(). Note that this should not be used to convert Unicode 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 consis- tent 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" statement-- this may change in future releases. 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
perlunicode, bytes perl v5.8.0 2002-06-01 utf8(3pm)