4.9 "C" A Programming Language

4.9 "C" A Programming Language

Most of the UNIX operating system is written in the "C" programming language. Most of the tools (and games) that run on the system are also written in "C". Many other utilities have a flavor of "C", such as the "C" shell csh, awk, and perl. The interface to the operating system is easily accessed with the "C" language. The operating system calls look like "C" function calls. The system calls are documented in section 2 of the manual pages. Library calls are documented in section 3 of the manual pages.

This lab will also be used to look at the effects of umask on protection bits when a file is created.

• Using a text editor, create the file hello.c with the following "C" program:

  /* Program to print "hello, world"                  */ 
  /* Kernighan & Richie "The C Programming Language"  */ 
  /* Copyright 1978  page 6                           */ 
  
  #include <stdio.h> 
  
  main() 
  { 
  printf("hello, world\n"); 
  }
  

• Compile and run the program: username@gort ~ $cc hello.c (cc is the standard C Compiler)
  or
  username@gort ~ $gcc hello.c (gcc is the gnu C Compiler) The standard output of the compiler is a.out. You can use the option -o to put the executable in another file.

  username@gort ~ $ ls -l a.out 
  -rwxrwxrwx   1 ltaber    15165 Oct 13 14:30 a.out
  

  username@gort ~ $a.out (run the program)

  hello, world                (resulting output)
  

   
• Now take a look at the effect of umask on file protection bits during file creation. You may have noted above that the protection bits that you saw on your a.out file did not match my example. This is because you may have a different umask setting. To look at your current setting try:

  username@gort ~ $ umask
  

  Your output should be an octal number that is the current setting for umask. If a bit is set in your umask it will prevent that bit from being set when a file is created. Set your umask to zero.

  username@gort ~ $ umask 0
  

  Recompile your program and look at the protection bits. It should now match my example. Now try a more restrictive setting:

  username@gort ~ $ umask 077
  

  Recompile your program and look at the protection bits for a.out again. This will only allow you to read, write, or execute the program. Your results should look like this:

  username@gort ~ $ ls -l a.out
  -rwx------   1 ltaber    15165 Oct 13 14:30 a.out
  

  Try a umask setting of 0777. Write on your lab what happens and explain why. I want you to turn in your explanation of what happened when you set your umask to 0777 and what you needed to do to get thing to work again.
• Create the file args.c with the following C program:

  
  /* Program to print arguments to a program    */ 
  /* L Taber   October 13, 1992   PCC           */ 
  
  #include <stdio.h> 
   
  main(argc, argv ) 
  int argc;
  char * argv[ ]; 
  
  {
  int i;
  
  printf("argc = %d   File name = %s\n", argc, argv[0]); 
  for ( i=1; i<argc; i++) 
      printf(" arg[%d] = %s\n" ,i,argv[i]); 
  printf("\n"); 
  } 
  

  Compile and test the program.
• Create the following script file "test1":

  #!/bin/bash
  #
  # L Taber  Argument passing
  # test script 
  a.out $@ 
  a.out $* 
  a.out "$@" 
  a.out "$*" 
  a.out '$@' 
  a.out '$*' 
  

• Test the script file.

  username@gort ~ $ test1 "A B" 'c d' e 
  

  The output should look as follows:

  argc = 6   File name = a.out
   arg[1] = A
   arg[2] = B
   arg[3] = c
   arg[4] = d
   arg[5] = e
  
  argc = 6   File name = a.out
   arg[1] = A
   arg[2] = B
   arg[3] = c
   arg[4] = d
   arg[5] = e
  
  argc = 4   File name = a.out
   arg[1] = A B
   arg[2] = c d
   arg[3] = e
  
  argc = 2   File name = a.out
   arg[1] = A B c d e
  
  argc = 2   File name = a.out
   arg[1] = $@
  
  argc = 2   File name = a.out
   arg[1] = $*
  

Turn in a copy of this output marked with:

your name 
TABER CIS137 
Lab 4.9: C Programming
Include your written explanation of what 
happened when you set umask to 0777 and
what was needed to get your account to function again.

Please turn your lab to Louis Taber or to Pima Community College employee in room A-115 of the Santa Rita Building. Ask them to place it in the dark blue folder in Louis Taber's mailbox.

4.9 "C" A Programming Language