Using the Process API — fork(), exec(), wait()

Build:

make

Run small demos:

make run

Q1 — fork() and variable x

After fork, child gets a copy-on-write address space. Both see initial x, but later writes are independent. See q1_fork_var.c.

Q2 — open()+fork() shared FD

Parent/child share the same open-file description, so writes interleave and share the file offset. See q2_open_fork.c (generates q2_output.txt).

Q3 — child prints first without wait()

Use a pipe: parent blocks on read until child signals. See q3_child_first_no_wait.c.

Q4 — exec variants

Demonstrates execl/execle/execlp/execv/execvp/execvpe (if available). See q4_exec_variants.c.

Q5 — wait()

In parent, wait() returns child's PID and fills status; in child, wait() fails with ECHILD. See q5_wait.c.

Q6 — waitpid()

Wait for a specific child (or use WNOHANG). Useful with multiple children. See q6_waitpid.c.

Q7 — close stdout in child

After closing fd 1, printf can't write to terminal; if a new file opens, it may reuse fd 1 -> output goes there. See q7_close_stdout.c.