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.




a == b


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.



Logical AND

a && b

Logical OR

a || b

Logical NOT

! a

Arithmetic operators





a + b

For string operands, this performs string concatenation.


a - b


a * b


a / b

For int or count operands, the fractional part of the result is dropped.


a % b

Operand types cannot be double.

Unary plus


Unary minus




Operand type cannot be double.



Operand type cannot be double.

Absolute value


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. The bitwise shift operators can also work with int. The bitwise complement operator works with count only.



Bitwise AND

a & b

Bitwise OR

a | b

Bitwise XOR

a ^ b

Bitwise left shift

a << b

Bitwise right shift

a >> b

Bitwise complement


Set operators



Set intersection

s1 & s2

Set union

s1 | s2

Set difference

s1 - s2

Assignment operators

The assignment operators evaluate to the result of the assignment.




a = b

Addition assignment (more generally, “add to”)

a += b

Subtraction assignment (more generally, “remove from”)

a -= b

Along with simple arithmetic, the += operator supports adding elements to table, set, vector, and pattern values, providing the righthand operand (RHS) has the same type. For table and set values, each of the RHS elements are added to the table or set. For vector, the RHS elements are appended to the end of the vector. For pattern values, the pattern is modified to include the RHS pattern as an alterantive (regular expression | operator).

The -= operator provides analogous functionality for table and set types, removing from the lefthand operand any elements it has in common with the RHS value. (Note that for tables, only the indices are used; if the RHS value has an index in common with the lefthand operand’s value, it’s removed even if the “yield” values differ.)

For all assignment operators, you can specify a comma-separated list of values within braces ({}). These are treated as constructor arguments to create a corresponding table, set, or vector value, with the type of constructor taken from the lefthand operand. For example:

local t: table[count, string] of double;
t += { [3, "three"] = 3.0, [9, "nine"] = 9.0 };

will add those two elements to the table t. For table and set constructors, you can embed lists in the constructor arguments to produce a cross-product expansion. For example:

local t: table[count, string] of double;
t += { [[3, 4], ["three", "four"]] = 3.0, [9, "nine"] = 9.0 };

results in t having five elements:

[3, three] = 3.0
[3, four] = 3.0
[4, three] = 3.0
[4, four] = 3.0
[9, nine] = 9.0

Finally, you can also use the += operator to append an element to the end of a vector. For example, v += e is equivalent to v[|v|] = e, providing that e’s type corresponds to that of one of v’s elements.

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.




Field access


Field value existence test


Evaluates to type bool. True if the specified field has been assigned a value, or if not.

Pattern operators

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




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.


p1 & p2

Evaluates to a pattern that represents matching p1 followed by p2.


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).




Type cast

v as t

Cast value v into type t. Evaluates to the value as cast 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 bool. 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 cast to their corresponding Zeek script types.

  • A value of declared type any can be cast to its actual underlying type.

  • All values can be cast 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




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


This operator can also be used with a set, but only with the add or delete statement.

Substring extraction


See the string type for more details.

Create a deep copy


This is relevant only for data types that are assigned by reference, such as vector, set, table, and record.

Module namespace access


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.


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. Known as the ternary operator.