bytes(3pm) Perl Programmers Reference Guide bytes(3pm)
NAME
bytes - Perl pragma to expose the individual bytes of characters
NOTICE
Because the bytes pragma breaks encapsulation (i.e. it exposes the
innards of how the perl executable currently happens to store a
string), the byte values that result are in an unspecified encoding.
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
Perl's characters are stored internally as sequences of one or more
bytes. This pragma allows for the examination of the individual bytes
that together comprise a character.
Originally the pragma was designed for the loftier goal of helping
incorporate Unicode into Perl, but the approach that used it was found
to be defective, and the one remaining legitimate use is for debugging
when you need to non-destructively examine characters' individual
bytes. Just insert this pragma temporarily, and remove it after the
debugging is finished.
The original usage can be accomplished by explicit (rather than this
pragma's implicit) encoding using the Encode module:
use Encode qw/encode/;
my $utf8_byte_string = encode "UTF8", $string;
my $latin1_byte_string = encode "Latin1", $string;
Or, if performance is needed and you are only interested in the UTF-8
representation:
utf8::encode(my $utf8_byte_string = $string);
"no bytes" can be used to reverse the effect of "use bytes" within the
current lexical scope.
As an example, when Perl sees "$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 (on
# ASCII platforms)"
}
"chr()", "ord()", "substr()", "index()" and "rindex()" behave
similarly.
For more on the implications, see perluniintro and perlunicode.
"bytes::length()" is admittedly handy if you need to know the byte
length of a Perl scalar. But a more modern way is:
use Encode 'encode';
length(encode('UTF-8', $scalar))
LIMITATIONS
"bytes::substr()" does not work as an lvalue().
SEE ALSO
perluniintro(1), perlunicode(1), utf8(3), Encode(3)
perl v5.30.3 2019-10-21 bytes(3pm)
perl 5.30.3 - Generated Fri Jun 5 14:21:37 CDT 2020