ans  =
 
    1.  
 
 
-->exec('Example3.sci')
 
-->clear
 
-->flag=1
 flag  =
 
    1.  
 
-->mode(-1)
Current date is 23-Jun-2013 
 
Welcome to the Textbook Companionship Project 2013 
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 Book Title                             :       UNIX CONCEPTS AND APPLICATIONS    
 
 Book Edition                         :                                                                           4   
 
 Book Author                          :                                                    Sumitabha Das   
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 Code Author                          :                                                     Pranav Bhat T   
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 Chapter Number                    :                                                                            24   
 
 Chapter Title                         :                              Systems programming II- Files   
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Example 3    :    Show the effect of changing the childs environment and check its effect in parent 
 
 ****************************************************************   
 
 Answer    :      
 
 INSTRUCTIONS   :    
  
 1.These programs are part of systems programming PURELY in Unix and the commands have NO EQUIVALENT IN SCILAB   
  
 2.However the .c files which are displayed here are also made into a seperate file.If you are a unix user then try compiling and 
       running the programme with gcc or cc compiler                                                                              
  
 3.The outputs displayed here are just MOCK OUTPUTS which are DISPLAYED IN THE TEXTBOOK   
  
 4.The inconvenience is regretted.   
.............Press [ENTER] to continue.....	UNIX SHELL SIMULATOR(DEMO VERSION WITH PRELOADED COMMANDS)




$ cat childenv.c      # to open the file emp.lst /* Program: childenv.c -- Changes child's environment and then checks the effect in parent*/
#include <stdio.h>
#include <sys/types.h>
#define PATH_LENGTH 30

int main(void) {
    pid_t pid;
    int x = 100;
    char newdir[PATH_LENGTH + 1]; /* Additional space required for \0*/
    
    getcwd(newdir, PATH_LENGTH);  /* Get current directory before fork */
    printf("BEFORE FORK -- Current directory: %s\n", newdir);
    
    pid = fork ();
    switch (pid) {
        case -1:
        perror("fork");
        exit(1);                /*for error*/
        case 0:  /*Child*/
        printf("CHILD -- Inherited value of x: %d\n", x);
        x=200;
        printf("CHILD -- Changed value of x: %d\n", x);
        printf("CHILD -- Inherited value of PATH: %s\n", getenv("PATH"));
        setenv("PATH",".", 1);   /* Change PATH here; use putenv("PATH=.") */
                                 /* if setenv() not supported */
        printf("CHILD -- New value of PATH: %s\n", getenv("PATH"));
        if (chdir("/etc") != -) {       /* "cd" to /etc */
        getcwd(newdir, PATH_LENGTH);    /* Do a "pwd" */
        printf("CHILD -- Current directory changed to: %s\n",newdir);
        }
        break;
        exit(0);
        default:/* Parent */
        sleep(2);                      /* Allow child to complete */
        getcwd(newdir, PATH_LENGTH);    /*Getting new directory */
        printf("PARENT -- Value of x after change by child: %d\n",x);
        printf("PARENT -- Current directory is still: %s\n", newdir);
        printf("PARENT -- Value of PATH is unchanged: %s\n",getenv("PATH"));
        exit(0);
}
}
 $ cc childenv.c $ a.out BEFORE FORK -- Current directory: /users1/home/staff/sumit
CHILD -- Inherited value of x: 100
CHILD -- Changed value of x:200
CHILD -- Inherited value of PATH: /usr/bin::/usr/local/bin:/usr/ccs/bin
CHILD -- New value of PATH: .
CHILD -- Current directory changed to: /etc
PARENT -- Value of x after change to child: 100
PARENT -- Current directory is still: /users1/home/staff/sumit
PARENT -- Value of PATH is unchanged: /usr/bin::/usr/local/bin::/usr/ccs/bin 


$ exit        #To exit the current simulation terminal and return to Scilab console

........# (hit [ENTER] for result)

			BACK TO SCILAB CONSOLE...
Loading initial environment 
 
-->diary(0)