Calling mpirun from bash file does not recognize $VAR format...?

While trying to run the following .sh file I get an error from mpirun: **The file: (additional python config omitted for brevity)** NB_MPI_WORKERS=2 SEED=0 mpirun --n ${NB_MPI_WORKERS} python start.py --base_path ~/temp --seed ${SEED} **The error:** Open MPI has detected that a parameter given to a command line option does not match the expected format: Option: n Param: 2 This is frequently caused by omitting to provide the parameter to an option that requires one. Please check the command line and try again. I have confirmed that simply replacing **${NB_MPI_WORKERS}** with **2** does work, so I'm a bit confused on where the error is, especially since ${seed} is working. Can anyone clarify, please? Is it actually an issue of formatting, or maybe type? Versions: - Linux Mint 20.2 - Open MPI 4.1.2