Operators¶

The Zeek scripting language supports the following operators. Note that each data type only supports a subset of these operators. For more details, see the documentation about the data types.

Relational operators¶

The relational operators evaluate to type `bool`.

In addition to numeric operands, the relational operators also work with operands of type `interval`, `time`, `string`, `port`, `addr`, and `set`.

Name Syntax
Equality a == b
Inequality a != b
Less than a < b
Less than or equal a <= b
Greater than a > b
Greater than or equal a >= b

Logical operators¶

The logical operators require operands of type `bool`, and evaluate to type `bool`.

Name Syntax
Logical AND a && b
Logical OR a || b
Logical NOT ! a

Arithmetic operators¶

Name Syntax Notes
Addition a + b For `string` operands, this performs string concatenation.
Subtraction a - b
Multiplication a * b
Division a / b For `int` or `count` operands, the fractional part of the result is dropped.
Modulo a % b Operand types cannot be “double”.
Unary plus + a
Unary minus - a
Pre-increment ++ a Operand type cannot be “double”.
Pre-decrement `--` a Operand type cannot be “double”.
Absolute value | a | If operand is `string`, `set`, `table`, or `vector`, this evaluates to number of elements.

Bitwise operators¶

The bitwise operators work with operands of type `count` or `vector of count`, but the bitwise complement operator works with `count` only.

Name Syntax
Bitwise AND a & b
Bitwise OR a | b
Bitwise XOR a ^ b
Bitwise complement ~ a

Set operators¶

Name Syntax
Set intersection s1 & s2
Set union s1 | s2
Set difference s1 - s2

Assignment operators¶

The assignment operators evaluate to the result of the assignment.

The “+=” operator can also be used to append an element to the end of a vector. For example, `v += e` is equivalent to `v[|v|] = e`.

Name Syntax
Assignment a = b
Addition assignment a += b
Subtraction assignment a -= b

Record field operators¶

The record field operators take a `record` as the first operand, and a field name as the second operand. For both operators, the specified field name must be in the declaration of the record type.

Name Syntax Notes
Field access a \$ b
Field value existence test a ?\$ b Evaluates to type `bool`. True if the specified field has been assigned a value, or false if not.

Pattern operators¶

In the table below, p is a pattern, and s is a string.

Name Syntax Notes
Exact matching p == s Evaluates to a boolean, indicating if the entire string exactly matches the pattern.
Embedded matching p in s Evaluates to a boolean, indicating if pattern is found somewhere in the string.
Conjunction p1 & p2 Evaluates to a pattern that represents matching p1 followed by p2.
Disjunction p1 | p2 Evaluates to a pattern that represents matching p1 or p2.

Type casting¶

The “as” operator performs type casting and the “is” operator checks if a type cast is supported or not. For both operators, the first operand is a value and the second operand is the name of a Zeek script type (either built-in or user-defined).

Name Syntax Notes
Type cast v as t Cast value “v” into type “t”. Evaluates to the value casted to the specified type. If this is not a supported cast, then a runtime error is triggered.
Check if a cast is supported v is t Evaluates to boolean. If true, then “v as t” would succeed.

Only the following kinds of type casts are supported currently:

• Broker values (i.e., `Broker::Data` values returned from functions such as `Broker::data`) can be casted to their corresponding Zeek script types.
• A value of declared type “any” can be casted to its actual underlying type.
• All values can be casted to their declared types (i.e., this is a no-op).

The function in this example tries to cast a value to a string:

```function example(a: any)
{
local s: string;

if ( a is string )
s = (a as string);
}
```

Other operators¶

Name Syntax Notes
Membership test a in b Evaluates to type `bool`. Works with `string`, `pattern`, `subnet`, `set`, `table`, or `vector` operands. Do not confuse this use of “in” with that used in a `for` statement.
Non-membership test a !in b This is the logical NOT of the “in” operator. For example: “a !in b” is equivalent to “!(a in b)”.
Table or vector element access a [ b ] This operator can also be used with a `set`, but only with the `add` or `delete` statement.
Substring extraction a [ b : c ] See the `string` type for more details.
Create a deep copy copy ( a ) This is relevant only for data types that are assigned by reference, such as `vector`, `set`, `table`, and `record`.
Module namespace access a :: b The first operand is the module name, and the second operand is an identifier that refers to a global variable, enumeration constant, or user-defined type that was exported from the module.
Conditional a ? b : c The first operand must evaluate to type `bool`. If true, then the second expression is evaluated and is the result of the entire expression. Otherwise, the third expression is evaluated and is the result of the entire expression. The types of the second and third operands must be compatible.