1. system.c  - call a program from a c program
2. execl.c   - exec a program in place of yourself 
3. execv.c   - exec a program in place of yourself, argv version 
4. fork0.c      - fork yourself
5. fork-sync.c  - fork and synchronize by waiting for a child.
6. forkexecl.c  - fork and exec, 
7. forkexecvp.c - fork and exec, argv version