NXLog Docs

Operators

Unary operators

The following unary operations are available. It is possible to use brackets around the operand to make it look like a function call as in the "defined" example below.

not

The not operator expects a boolean value. It will evaluate to undef if the value is undefined. If it receives an unknown value that evaluates to a non-boolean, it will result in a run-time execution error.

Example 1. Using the "not" Operand

If the $Success field has a value of false, an error is logged.

if not $Success log_error("Job failed");
defined

The defined operator will evaluate to TRUE if the operand is defined, otherwise FALSE.

Example 2. Using the Unary "defined" Operation

This statement is a no-op, it does nothing.

if defined undef log_info("never printed");

If the $EventTime field has not been set (due perhaps to failed parsing), it will be set to the current time.

if not defined($EventTime) $EventTime = now();

Binary operators

The following binary operations are available.

The operations are described with the following syntax:

LEFT_OPERAND_TYPE OPERATION RIGHT_OPERAND_TYPE = EVALUATED_VALUE_TYPE

=~

This is the regular expression match operation as in Perl. This operation takes a string and a regular expression operand and evaluates to a boolean value which will be TRUE if the regular expression matches the subject string. Captured sub-strings are accessible through numeric reference (such as $1) and the full subject string is placed into $0. Regular expression-based string substitution is supported with the s/// operator. For more details, see Regular Expressions.

Example 3. Regular Expression String Matching

A log message will be generated if the $Message field matches the regular expression.

if $Message =~ /^Test message/ log_info("matched");
!~

This is the opposite of =~

The expression will evaluate to TRUE if the regular expression does not match on the subject string. It can be also written as not LEFT_OPERAND =~ RIGHT_OPERAND. The s/// substitution operator is supported.

Example 4. Regular Expression Based Negative String Matching

A log message will be generated if the $Message field does not match the regular expression.

if $Message !~ /^Test message/ log_info("didn't match");
==

This operator compares two values for equality. Comparing a defined value with an undefined results in undef.

Example 5. Equality

A log message will be generated if $SeverityValue is 1.

if $SeverityValue == 1 log_info("severity is one");
!=

This operator compares two values for inequality. Comparing a defined value with an undefined results in undef.

Example 6. Inequality

A log message will be generated if $SeverityValue is not 1.

if $SeverityValue != 1 log_info("severity is not one");
<

This operation will evaluate to TRUE if the left operand is less than the right operand, and FALSE otherwise. Comparing a defined value with an undefined results in undef.

Example 7. Less

A log message will be generated if $SeverityValue is less than 1.

if $SeverityValue < 1 log_info("severity is less than one");
<=

This operation will evaluate to TRUE if the left operand is less than or equal to the right operand, and FALSE otherwise. Comparing a defined value with an undefined results in undef.

Example 8. Less or Equal

A log message will be generated if $SeverityValue is less than or equal to 1.

if $SeverityValue < 1 log_info("severity is less than or equal to one");
>

This operation will evaluate to TRUE if the left operand is greater than the right operand, and FALSE otherwise. Comparing a defined value with an undefined results in undef.

Example 9. Greater

A log message will be generated if $SeverityValue is greater than 1.

if $SeverityValue > 1 log_info("severity is greater than one");
>=

This operation will evaluate to TRUE if the left operand is greater than or equal to the right operand, and FALSE otherwise. Comparing a defined value with an undefined results in undef.

Example 10. Greater or Equal

A log message will be generated if $SeverityValue is greater than or equal to 1.

if $SeverityValue >= 1 log_info("severity is greater than or equal to one");
and

This operation evaluates to TRUE if and only if both operands are TRUE. The operation will evaluate to undef if either operand is undefined.

Example 11. And Operation

A log message will be generated only if both $SeverityValue equals 1 and $FacilityValue equals 2.

if $SeverityValue == 1 and $FacilityValue == 2 log_info("1 and 2");
or

This operation evaluates to TRUE if either operand is TRUE. The operation will evaluate to undef if both operands are undefined.

Example 12. Or Operation

A log message will be generated if $SeverityValue is equal to either 1 or 2.

if $SeverityValue == 1 or $SeverityValue == 2 log_info("1 or 2");
+

This operation will result in an integer if both operands are integers. If either operand is a string, the result will be a string where non-string typed values are converted to strings. In this case it acts as a concatenation operator, like the dot (.) operator in Perl. Adding an undefined value to a non-string will result in undef.

Example 13. Concatenation

This statement will always cause a log message to be generated.

if 1 + "a" == "1a" log_info("this will be printed");
-

Subtraction. The result will be undef if either operand is undefined.

Example 14. Subtraction

This statement will always cause a log message to be generated.

if 4 - 1 == 3 log_info("four minus one is three");
*

Multiply an integer with another. The result will be undef if either operand is undefined.

Example 15. Multiplication

This statement will always cause a log message to be generated.

if 4 * 2 == 8 log_info("four times two is eight");
/

Divide an integer with another. The result will be undef if either operand is undefined. Since the result is an integer, a fractional part is lost.

Example 16. Division

This statement will always cause a log message to be generated.

if 9 / 4 == 2 log_info("9 divided by 4 is 2");
%

The modulo operation divides an integer with another and returns the remainder. The result will be undef if either operand is undefined.

Example 17. Modulo

This statement will always cause a log message to be generated.

if 3 % 2 == 1 log_info("three mod two is one");
IN

This operation will evaluate to TRUE if the left operand is equal to any of the expressions in the list on the right, and FALSE otherwise. Comparing a undefined value results in undef.

Example 18. IN

A log message will be generated if $EventID is equal to any one of the values in the list.

if $EventID IN (1000, 1001, 1004, 4001) log_info("EventID found");
NOT IN

This operation is equivalent to NOT expr IN expr_list.

unknown NOT IN unknown, unknown …​ = boolean

Example 19. NOT IN

A log message will be generated if $EventID is not equal to any of the values in the list.

if $EventID NOT IN (1000, 1001, 1004, 4001) log_info("EventID not in list");

Ternary operators

The ternary operator expr1 ? expr2 : expr3 evaluates to expr2 if expr1 is TRUE, otherwise to expr3. The parentheses as shown here are optional.

Example 20. Using the Ternary Operator

The $Important field is set to TRUE if $SeverityValue is greater than 2, or FALSE otherwise.

$Important = ( $SeverityValue > 2 ? TRUE : FALSE );