Makefile- creates an executable shell file when "make" is typed sh257- an executable file that is created after make command csapp.h- a declared collection of auxiliary functions that include utility functions for Unix file i/o, sockets, signals, threads, and semaphores. csapp.c- defined functions for the utility functions for Unix file i/o, sockets, signals, threads, and semaphores. csapp.o- object file created for csapp.c after compiling, so manual recompilation of csapp.c file is not required when "make" is typed shellex.c- contains main code for creating each custom shell command. shellex.o- object file for shellex.c