Many possibilities:
- use as a simple calculator with vectors, tensors etc.
- test validity of expression syntax

As a calculator:

    foamCalc  '(vector(1,2,3) ^ vector(4,5,6)) * sqrt(34)'

The same, but with debugging:

    foamCalc -debug-switch fieldExpr=6 \
        'mag((vector(1,2,3) ^ vector(4,5,6))) * sqrt(34)'