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3.13. Bitwise Operators
Like C, Perl has bitwise AND, OR, and XOR (exclusive OR) operators:
&, |, and ^. You''ll have noticed from your painstaking
examination of the table at the start of this chapter that bitwise AND
has a higher precedence than the others, but we''ve cheated and combined
them in this discussion.
These operators work differently on numeric values than they do on
strings. (This is one of the few places where Perl cares about the
difference.) If either operand is a number (or has been used as a
number), both operands are converted to integers, and the
bitwise operation is performed between the two integers. These
integers are guaranteed to be at least 32 bits long, but can be 64 bits
on some machines. The point is that there''s an arbitrary limit imposed
by the machine''s architecture.If both operands are strings (and have not been used as numbers since
they were set), the operators do bitwise operations between corresponding
bits from the two strings. In this case, there''s no arbitrary limit,
since strings aren''t arbitrarily limited in size. If one string is
longer than the other, the shorter string is considered to have a
sufficient number of 0 bits on the end to make up the difference.For example, if you AND together two strings:
"123.45" & "234.56"
you get another string:
"020.44"
But if you AND together a string and a number:
"123.45" & 234.56
The string is first converted to a number, giving:
123.45 & 234.56
The numbers are then converted to integers:
123 & 234
which evaluates to 106. Note that all bit strings are true (unless
they result in the string "0"). This means if you
want to see whether any byte came out to nonzero, instead of writing
this:
if ( "fred" & "\1\2\3\4" ) { ... }
you need to write this:
if ( ("fred" & "\1\2\3\4") =~ /[^\0]/ ) { ... }
