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incr - Increment the value of a variable
incr varName ?increment? _________________________________________________________________
Increments the value stored in the variable whose name is varName. The value of the variable must be an integer. If increment is supplied then its value (which must be an integer) is added to the value of variable varName; otherwise 1 is added to varName. The new value is stored as a decimal string in variable varName and also returned as result.
add, increment, variable, value