This is makeindex, version 2.15 [TeX Live 2020] (kpathsea + Thai support).
Scanning style file ./main.ist.............................done (29 attributes redefined, 0 ignored).
Scanning input file main.bsn....done (103 entries accepted, 0 rejected).
Sorting entries....done (763 comparisons).
Generating output file main.bsd....done (79 lines written, 0 warnings).
Output written in main.bsd.
Transcript written in main.bsg.