Larry-
 Assuming you ran a study with multiple individuals who each had a T1, DTI and fMRI scan, and all their DICOM files were in a single folder, you could convert these from the command line (or MRIcroGL's graphical interface) using a command like
  dcm2niix -f %t_%p_%s ~/dicomDir
This will generate NIfTI images where the filename includes study time (%t), protocol name (%p) and series number (%s). So an output mike look like 
  201712120100_T1_2
where the time tells provides the protocol tells you the modality, and the series number helps you distinguish multiple fMRI runs. If this solution is acceptable, you do not need a script at all. Likewise, you can wrap this command in your favorite scripting language (Python, Matlab, shell, etc).

Another option might be to convert your DICOM data to NIfTI data in a BIDS structure. There are a number of scripts that will allow you to do this. For example, see the "Links" section of the dcm2niix github page
  https://github.com/rordenlab/dcm2niix