FLASH constructs the output filenames based on the user-supplied basename, (runtime parameter basenm) and the file counter that is incremented after each output. Additionally, information about the file type and data storage is included in the filename. The general checkpoint filename is:
where hdf5 or ncmpi (prefix for PnetCDF) is picked depending on the particular IO implementation, the number following the ``s'' is the split file number, if split file IO is in use, and the number at the end of the filename is the current checkpointFileNumber. (The PnetCDF function prefix "ncmpi" derived from the serial NetCDF calls beginning with "nc")
The general plotfile filename is:
basename_s0000_ _plt_ _0000,
where hdf5 or ncmpi is picked depending on the IO implementation used, crn and cnt indicate data stored at the cell corners or centers respectively, the number following ``s'' is the split file number, if used, and the number at the end of the filename is the current value of plotfileNumber. crn is reserved, even though corner data output is not presently supported by FLASH4's IO.
Generic Flash Docs User 2019-10-18