Section: Perl Programmers Reference Guide (3pm)
Updated: 2001-09-21
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bytes - Perl pragma to force byte semantics rather than character semantics  


    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;



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.  


bytes::substr() does not work as an lvalue().  


perluniintro, perlunicode, utf8



SEE ALSO manual pages