In order to run MOPAC calculations interactively from the command line you have to:
1) Create a MOPAC input file. The name of this file must end in ".dat"
2) Run the job by typing mopac2 input file
Please observe that the name of the input file must in this case be given without the .dat ending. If, for example, your input file is testit1.dat, the calculation can be started by typing mopac2 testit1. Keep in mind that MOPAC will generate a number of temporary files during execution in the current working directory. You can therefore only run one MOPAC job at a time in a single directory.