1.7. Operators
NASL
provides arithmetic, comparison, and assignment operators. These
operators are explained in the following sections.
1.7.1. 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.
1.7.2. 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.
1.7.3. 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.
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