General purpose, formatter-independent index processor
The program makeindex is a general purpose hierarchical index generator; it accepts one or more input files (often produced by a text formatter such as TeX or troff, sorts the entries, and produces an output file which can be formatted. The index can have up to three levels (0, 1, and 2) of subitem nesting. The way in which words are flagged for indexing within the main document is specific to the formatter used; makeindex does not automate the process of selecting these words. As the output index is hierarchical, makeindex can be considered complementary to the awk(1)-based make.index(1L) system of Bentley and Kernighan, which is specific to troff(1), generates non-hierarchical indices, and employs a much simpler syntax for indicating index entries.
pkg install makeindex