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NMIS version 8.4.8G and later support modelling such scenarios using custom variables, or CVARs. With this mechanism you can temporarily capture up to 10 separate SNMP properties as a CVAR and define an arbitrarily complex expression (in perl) that transforms these CVARs into the one measurement that you want to collect and/or display.

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In both cases the syntax is very straight-forward:

• The expression must be a valid perl statement and return exactly one value.
• The tokens $r, and CVAR0 to CVAR9 are interpreted by NMIS; everything else is perl.
• Defining and using local variables with my is ok, but don't attempt to change any global NMIS variables.
• "CVAR1=some_snmp_var;" defines what SNMP object CVAR1 is supposed to hold. The parser understands CVAR0 to CVAR9 for a total of 10 captures.
• "return $r/$CVAR1;" accesses the value of CVAR1 in an expression. The variable "$r" represents the SNMP variable that the calculate expression is attached to.
  
  

Please note that the $CVARn replacement in the expression is performed on a purely textual basis, before the expression is handed to the perl interpreter for evaluation :

• For string variables you have to provide quotes in your expression, e.

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• g.

  Code Block
  calculate => 'CVAR1=somestringthing; return 42 if ("$CVAR1" eq "online");'

• Numeric variables can be used straight without quotes.