(1) show initial shell (sh0.c)
    gcc sh0.c -o sh0
    ./sh0
    $ /bin/ls

(2) cp sh0.c sh1.c
    modify sh1.c, inserting before the execv():

	close(1);
	creat("tmp1", 0666);

    gcc sh1.c -o sh1
    ./sh1
    $ /bin/ls
    $ ^D
    cat tmp1

(3) create file ./script:

	/bin/echo one
	/bin/echo two

    ./sh0 < script
    ./sh0 < script > tmp1
    cat tmp1

(4) ./sh1
    $ /bin/ls sh0.c sh2.c shx.c
    $ ^D
    cat tmp1

    modify sh1.c, inserting after creat():

	close(2);
	creat("tmp1", 0666);

    gcc sh1.c -o sh1
    ./sh1
    $ /bin/ls sh0.c sh2.c shx.c
    $ ^D
    cat tmp1

    modify sh1.c again, replacing the second creat() with dup(1)

    gcc sh1.c -o sh1
    ./sh1
    $ /bin/ls sh0.c sh2.c shx.c
    $ ^D
    cat tmp1

(5) ssh 32bit-linux-box
    linux% cd /proc/$$
    linux% pwd
    linux% ls -l

    linux% cat maps
    linux% ls -l fd

    linux% exec 5>/tmp/out5
    linux% ls -l fd

    linux% exec 1>/tmp/out1
    linux% ls -l fd
    linux% exec 1>&0
    linux% cat /tmp/out1

    linux% exec 5>&-
    linux% ls -l fd
    linux% 

(6) cat file.txt
    sort < file.txt
    sort < file.txt | uniq
    sort < file.txt | uniq | wc -l

(7) show pipe.c
    gcc pipe.c -o pipe
    ./pipe

(8) add to pipe.c:

	  pipe(fdarray)
	+ int pid = fork();
	+ if (pid == 0) {
	    write(fdarray[1], "hello", 5);
	+ } else {
	    n = read(fdarray[0], buf, sizeof(buf));
	    printf("%d bytes: %.*s\n", n, n, buf);
	+ }

    gcc pipe.c -o pipe
    ./pipe

(9) show sh2.c
    gcc sh2.c -o sh2
    ./sh2
    $ /bin/sort file.txt | /bin/uniq
    $