Operator Precedence

The logical operators && and || both return the value that makes them true, not just a boolean true or false. For example, &Foo := (User-Password || "help") returns the value of User-Password if it exists, or else the string "help" if it does not.

If a math operation causes an overflow, underflow, or division by zero, it returns no result. This impacts the rest of the calculation. You can use the || operator to replace a missing result with a different value.

Use parentheses ( ) to wrap a nested expression. They also help clarify policies and define the order of evaluation.

The following tables summarises the order of precedence of the v4 operators.

Table 1. Operator Precedence in Conditional Expressions
Priority	Operator(s)	Category	Notes
1 (highest)	`( )`	Grouping	Overrides all other precedence.
2	`!` `-`	Logical NOT / Unary	Prefix negation; also bitwise `~` for integers.
3	`^`	XOR
4	`*` `/` `%`	Arithmetic	Standard multiply, divide, modulo.
5	`+` `-`	Arithmetic	Addition/subtraction and also string/octet concatenation.
6	`<<` `>>`	Bitwise shift left/right	bit shift
8	`\|`	Binary OR	Also string/octet OR
7	`&`	Binary AND	Also works on `ipv4addr`/`string`/`octet` types.
9	`==` `!=` `<` `>` `⇐` `>=` `=~` `!~`	Comparison	Produces a boolean result. The `=~` and `!~` are produce regex results.
10	&&	Logical AND	Short-circuits and also returns the value that caused success.
11 (lowest)	`\|\|`	Logical OR	Short-circuits and can also be used to replace null results.

The %{expr:…} syntax is not supported in v4 and will return an error. You can now use math directly inside conditions and double-quoted strings.