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Return values of commands

The command trace is used to retrieve the return value of a command. Some of the builtin commands return 0 if they have been successfully executed or 0 in an error has been detected.

- interpcom -> trace 1

turns on the trace of return values of commands. The return value of subsequent commands will then be put in the variable retval of the expression evaluator. To stop the trace of return values, simply do

- interpcom -> trace 0