Perl in a Nutshell, 2nd Edition

Unary Operators

Unary ! performs logical negation, that is, “not.” The not operator is a lower-precedence version of !.

Unary - performs arithmetic negation if the operand is numeric. If the operand is an identifier, then a string consisting of a minus sign concatenated with the identifier is returned. Otherwise, if the string starts with a plus or minus, a string starting with the opposite sign is returned.

Unary ~ performs bitwise negation, that is, one’s complement. For example, on a 32-bit machine, ~0xFF is 0xFFFFFF00. If the argument to ~ is a string instead of a number, a string of identical length is returned, but with all the bits of the string complemented.

Unary + has no semantic effect whatsoever, even on strings. It is syntactically useful for separating a function name from a parenthesized expression that would otherwise be interpreted as the complete list of function arguments.

Unary \ creates a reference to whatever follows it (see Section 4.8 later in this chapter). Do not confuse this behavior with the behavior of the backslash within a string. The \ operator may also be used on a parenthesized list value in a list context, in which case it returns references to each element of the list.