Due: 9/12/2001 - Class Time

You should review in the man pages

• open
• fopen
• dup
• dup2

Write a C program (Prog4a.c) that mimics the program cat. i.e.

while (not EOF of stdin)
     scanf(the content of stdin)
     printf(everything read by scanf) 

Write a C program (Prog4b.c) that will accept command line arguments of the following types

ShellPrompt> Prog4b Prog4a

1. this means that Prog4b should fork() and exec(Prog4a).
2. Prog4b should wait() for 4a to exit() before it exit()s

ShellPrompt> Prog4b Prog4a < fileABC

1. prior to the step #2, 4b should
   • open fileABC for input
   • modify the fd-Table such that 4b will scanf fileABC as stdin
2. 4b should fork() and exec(4a).
3. 4b should wait() for 4a to exit() before it exit()s

ShellPrompt> Prog4b Prog4a < fileABC > fileXYZ

1. prior to the step #2, 4b should
   • open fileABC for input
   • modify the fd-Table such that 4b will scanf fileABC as stdin
   • open fileXYZ for output
   • modify the fd-Table such that 4b will printf fileXYZ as stdout
2. 4b should fork() and exec(4a).
3. 4b should wait() for 4a to exit() before it exit()s

ShellPrompt> Prog4b Prog4a > fileXYZ

1. prior to the step #2, 4b should
   • open fileXYZ for output
   • modify the fd-Table such that 4b will printf fileXYZ as stdout
2. 4b should fork() and exec(4a).
3. 4b should wait() for 4a to exit() before it exit()s

=================================================================

NOTEs:

• The shell will want to interpret the '<' and '>' as file redirection requests that IT should carry out. Prevent the shell from doing this by either escaping them as \> and \< or quoting them as '>' and '<' or quoting the entire command line argument.
• You may surround the operators (< and >) with spaces.
• You may assume that Prog4b will always see argv[1] = Prog4a
• You may dispense with the command line arguments completely and let Prog4b
  1. Read a line
  2. Carry out the fd manipulation, fork, exec, wait
  3. Go back to #1

You should use the 'script' command to capture all necessary information for handin.