Operator Precedence and Associativity
Operator precedence determines which operators in a complex expression are evaluated first. Associativity determines how operators that have the same precedence are evaluated (where your choices are left-to-right, right-to-left, or nonassociative for those operators where order of evaluation is either not important, not guaranteed, or not even possible). Table 3.2 shows the precedence and associativity of the various operators available in Perl, with operators of a higher precedence (evaluated first) higher up in the table than those of a lower precedence (evaluated later). You'll want to fold down the corner of this page or mark it with a sticky note; this is one of those tables you'll probably refer to over and over again as you work with Perl.
You can always change the evaluation of an expression (or just make it easier to read) by enclosing it with parentheses. Expressions inside parentheses are evaluated before those outside parentheses.
Note that there are a number of operators in this table you haven't learned about yet (and some I won't cover in this book at all). I've included lesson references for those operators I do explain later on in this book.
| Operator | Associativity | What it means |
|---|---|---|
| -> | left | Dereference operator (Day 19, “Working with References” |
| ++ -- | non | Increment and decrement |
| ** | right | Exponent |
| ! ~ + - | right | Logical not, bitwise not, reference (Day 19), unary +, unary - |
| =~ !~ | left | Pattern matching |
| * / % x | left | Multiplication, division, modulus, string repeat |
| + - . | left | Add, subtract, string concatenate |
| << >> | left | Bitwise left shift and right shift |
| unary operators | non | Function-like operators (See today's “Going Deeper” section) |
| < > <= >= lt gt le ge | non | Tests |
| == != <=> eq ne cmp | non | More tests (<=> and cmp, Day 8, “Data Manipulation with Lists”) |
| & | left | Bitwise AND |
| | ^ | left | Bitwise OR, bitwise XOR |
| && | left | C-style logical AND |
| || | left | C-style logical OR |
| .. | non | Range operator (Day 4, “Working with Lists and Arrays”) |
| ?: | right | Conditional operator (Day 6, “Conditionals and Loops”) |
| = += -= *= /=, etc. | right | Assignment operators |
| , => | left | Comma operators (Day 4) |
| list operators | non | list operators in list context (Day 4) |
| not | right | Perl logical NOT |
| and | left | Perl logical AND |
| or xor | left | Perl logical OR and XOR |