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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superseded.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, "\n"; # "Length is 1"
printf "Contents are %vd\n", $x; # "Contents are 400"
{
use bytes; # or "require bytes; bytes::length()"
print "Length is ", length $x, "\n"; # "Length is 2"
printf "Contents are %vd\n", $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 v5.20.2 2014-12-27 bytes(3perl)
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