4.5.1 The Arrow Operator

The arrow operator is a dereference operator. It can be used for references to arrays, hashes, code references, or for calling methods on objects. See the discussion of references in Chapter 7, Packages, Modules, and Objects.

4.5.2 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 "References and Complex Data Structures" later in this chapter). Do not confuse this behavior with the behavior of 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.

4.5.3 Arithmetic Operators

Binary ** is the exponentiation operator. Note that it binds even more tightly than unary minus, so -2**4 is -(2**4), not (-2)**4. Note also that ** has right associativity, so:

$e = 2 ** 3 ** 4;

The * (multiply) and / (divide) operators work exactly as you might expect, multiplying or dividing their two operands. Division is done in floating-point mode, unless integer mode in enabled (via use integer).

The % (modulus) operator converts its operands to integers before finding the remainder according to integer division. For the same operation in floating-point mode, you may prefer to use the fmod() function from the POSIX module (see Chapter 8).

4.5.4 Comparison Operators

4.5.5 Autoincrement and Autodecrement

If placed before a variable, the ++ and -- operators increment or decrement the variable before returning the value, and if placed after, they increment or decrement the variable after returning the value.

4.5.6 Assignment Operators

Perl recognizes the following operators for assigning a value to a variable:

=    **=    +=    *=    &=    <<=    &&=
            -=    /=    |=    >>=    ||=
            .=    %=    ^=
                  x=

$var OP= $value

$var = $var OP $value

$a += 2; # same as $a = $a + 2

4.5.7 Pattern Match Operators

Binary =~ binds a scalar expression to a pattern match, substitution, or translation. These operations search or modify the string $_ by default.

Binary !~ is just like =~ except the return value is negated in the logical sense. The following expressions are functionally equivalent:

$string !~ /pattern/
not $string =~ /pattern/

4.5.8 File Test Operators

A file test operator is a unary operator that tests a filename or a filehandle.

4.5.9 Logical Operators

Perl provides the && (logical AND) and || (logical OR) operators. They evaluate from left to right testing the truth of the statement.

For example, an oft-appearing idiom in Perl programs is:

open(FILE, "somefile") || die "Cannot open somefile: $!\n";

Perl also provides lower-precedence and and or operators that are more readable.

4.5.10 Bitwise Operators

Perl has bitwise AND, OR, and XOR (exclusive OR) operators: &, |, and ^. These operators work differently on numeric values than they do on strings. If either operand is a number, then both operands are converted to integers, and the bitwise operation is performed between the two integers. If both operands are strings, these operators do bitwise operations between corresponding bits from the two strings.

4.5.11 Miscellaneous Operators