CS208 Introduction to Computer Systems
Friday, 7 November 2025

+ Command shell steps (assume no > or |)
- print prompt
- read user's command
- fork
    - child
        - build argv and argc
        - execvp
    - parent
        - wait for child to terminate
- parent's wait is over
- go to beginning

+ Sample programs
- forktest.c
- exectest.c
- argv.c
- exectest_with_args.c
- tokenizer assignment (but NOTE THE NULL at the end of argv[])

+ Command shell steps: "command > file"
...
    - child
        - build argv and argc
        - redirect stdout to file  <---
        - execvp
...

+ Sample programs
- files.c
- redirection.c

+ Command shell steps: "command1 | command2"
PLAN
- parent forks to create child1 (for command1)
- parent forks again to create child2 (for command2)
- child1 redirects its own stdout
- child2 redirects its own stdin

FLOW
- print prompt
- read user's command line
[execute_command]
- notice the |
[call the "do pipe command" function]
- create a pipe
- fork
    - child
        - build argv and argc (stopping at |)
        - redirect stdout to write-end of the pipe
        - execvp
    - parent
        - fork
            - child
                - build argv and arc (starting just after |)
                - redirect stdin to read-end of the pipe
                - execvp
            - parent
                - wait for child to terminate
                - wait for child to terminate

- parent's waits are over
- go to beginning

+ Sample programs
- pipe.c

+ One more sample program
- shell208.c