This very old UNIX source code from 1979. This is source code for the Bourne shell. This code looks alien compared to modern C code, I wonder if it would even compile on a modern machine.
Have a look here: https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/expand.c.
But I installed all the include files and it would not compile on Kali Linux, code from 1979 will not work on a modern PC. But this was fun anyway. The old C code needs too much work to function on Modern Linux machines.
This is all of the errors I got when trying to compile this source code on Kali Linux 2019.