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Comment: updated CVARx details


  • 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.
  • You can use functions that were defined elsewhere in NMIS in your calculate expression.
    You will likely have to include the full module namespace in the function call, e.g. func::beautify_physaddress(...).
    Only functions without side-effects should be used.
  • "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.g.

      Code Block
      calculate => 'CVAR1=somestringthing; return 42 if ("$CVAR1" eq "online");'
    • Numeric variables can be used straight without quotes.
  • the $CVARn access refers to the raw value of the named property, ie. the data before any replace or calculate expressions for the named property were evaluated.

How to keep temporary CVAR data out of the RRD databases