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Extensions for LUA language

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Scientific calculator and inline script

The second way of using LUA script language in the expression of Active View graphical object is called inline. The expression of a graphical object can be a LUA script including SNMP Get command mixed with mathematical functions.

The syntax of the expression is:

Getipoid defip LUA_expression

example : getipoid defip ([hrstorageused.3]/[hrstoragesize.3]*100)

The LUA expression can contain multiple snmp requests. Each snmp request should be in brackets [] in the LUA expression. , other mathematical operator in parenthesis. To know what operators are available open the LUA 5.0 reference manual.

The object [$lastvalue] replace the string of by the last value obtained from this expression. This option is useful when working with counter snmp objects.

Example of expression:

  1. Display the disk utilization in percentage of the total disk space. The SNMP object used are defined in the host-resource-mib.

    getipoid defip ([hrstorageused.3]/[hrstoragesize.3]*100)

  2. Display the disk utilization in Mega bytes.

    getipoid defip ((([hrStorageSize.3]-[hrstorageused.3])*[hrstorageallocationunits.3])/1024)/1024

warning : avoid space in the script expression

Correct : (([hrstorageused.3]/[hrstoragesize.3]*100)/1000)

Not recommended (The LUA expression parser support only 50 blocks)

( ( [hrstorageused.3] / [hrstoragesize.3] * 100 ) / 1000)


This expression return a value

#ERROR if the syntax is wrong or if the snmp object are not found
1.#INF00 If there is divided by zero operation in the script

We are working on a VuMeter object, this one has a Unit field in its properties. If the option "Fill name" is checked the unit will be automatically added at this end of the object name in the view.

The fill name option replace the object name visible in the view.
The unit option is added to the name

VuMeter Unit

In the Active View below you can see the disk size directly displayed in the object name.


In the next example we use a virtual snmp objet to perform a calculation

This example use a sinus funtion.

Mathematical functions are listed in this LUA documentation extract:

This library is an interface to most of the functions of the standard C math library. (Some have slightly different names.) It provides all its functions inside the table math. In addition, it registers the global __pow for the binary exponentiation operator ^, so that x^y returns xy. The library provides the following functions:

math.abs

Absolute value
math.acos Arc Cosinus
math.asin Arc Sinus
math.atan Arc Tangente
math.atan2  
math.ceil  
math.cos Cosinus
math.deg convert to degrees
math.exp Exponential
math.floor  
math.log Logarithm
math.log10 Logarithm 10
math.max The function math.max returns the maximum value of its numeric argument
math.min math.min computes the minimum. Both can be used with 1, 2, or more arguments.
math.mod Modulo
math.pow  
math.rad convert to radian
math.sin SiInus
math.sqrt Square root
math.tan Tangente
math.frexp  
math.ldexp  
math.random Generate a random number :The functions math.random and math.randomseed are interfaces to the simple random generator functions rand and srand that are provided by ANSI C. (No guarantees can be given for their statistical properties.) When called without arguments, math.random returns a pseudo-random real number in the range [0,1). When called with a number n, math.random returns a pseudo-random integer in the range [1,n]. When called with two arguments, l and u, math.random returns a pseudo-random integer in the range [l,u]. The math.randomseed function sets a "seed" for the pseudo-random generator: Equal seeds produce equal sequences of numbers.
math.randomseed  
math.pi and the PI variable

Most of them are only interfaces to the corresponding functions in the C library. All trigonometric functions work in radians (previous versions of Lua used degrees). The functions math.deg and math.rad convert between radians and degrees.
s.


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