Operators

NASL provides arithmetic, comparison, and assignment operators. These operators are explained in the following sections.

Arithmetic Operators

Here are the common arithmetic operators:

+Used to add numbers. It can also be used to perform string concatenation.

-Used to perform subtraction. It can also be used to perform string subtraction. For example, ‘cat, dog, mouse’ – ‘, dog’ results in the string ‘cat, mouse’.

*Used to multiply numbers.

/Used to divide numbers. Note that NASL will return a 0 if you try to divide by zero.

%Used to perform a modulo operation. For example, 10%3 computes to 1.

**Used to perform exponentiation. For example, 2**3 computes to 8.

++Used to increment a variable’s value by 1. When a variable is prefixed by this operator (example: ++c), its value is incremented before it is evaluated. When a variable is post-fixed by this operator (example: c++), its value is incremented after it is evaluated.

—Used to decrement a variable’s value by 1. When a variable is prefixed by this operator (example: –c), its value is decremented before it is evaluated. When a variable is post-fixed by this operator (example: c–), its value is decremented after it is evaluated.

Comparison Operators

Here are the common comparison operators:

>Used to test whether a given value is greater than the other.

>=Used to test whether a given value is greater than or equal to the other.

<Used to test whether a given value is less than the other.

<=Used to test whether a given value is less than or equal to the other.

==Used to test whether a given value is equal to the other.

!=Used to test whether a given value is not equal to the other.

><Used to test whether a given substring exists within a string. For example, ‘123’><‘abcd123def’ evaluates to TRUE.

>!<Used to test whether a given substring does not exist within a string. In this case, ‘123’>!<‘abcd123def’ evaluates to FALSE.

=~Used to match a regular expression. Using this operator is similar to calling the ereg( ) function call, which performs a similar operation. For example, the statement str =~ ‘^[GET / HTTP/1.0\r\n\r\n][.]*’) evaluates to TRUE only if str begins with the string GET / HTTP/1.0\r\n\r\n.

!~Used to test whether a regular expression does not match. It is the opposite of the =~ operator.

[]Used to select a character from a string by index. For example, if mystring is a1b2c3, mystring[3] evaluates to 2.

Assignment Operators

Here are the common assignment operators:

=Used to assign a value to a variable.

+=Used to increment a variable’s value. For example, a += 3 increments the value of a by 3, and is equivalent to the statement a = a + 3.

-=Used to decrement a variable’s value. For example, a -=3 decrements the value of a by 3, and is equivalent to the statement a = a – 3.

*=Used to multiply a variable’s value by a specified value. For example, a *= 3 causes the variable a to be assigned a value equal to itself multiplied by 3, and is equivalent to the statement a = a * 3.

/=Used to divide a variable’s value by a specified value. For example, a /=3 causes the variable a to be assigned a value equal to itself divided by 3, and is equivalent to the statement a = a / 3.

%=Used to assign a variable a value equal to the remainder of a division operation between itself and a specified value. For example, a %=3 causes the variable a to be assigned a value that is equal to the remainder of the operation a/3, and is equivalent to the statement a = a % 3.