ans  =
 
    1.  
 
-->exec('Example6.sci')
 
-->clear
 
-->flag=1
 flag  =
 
    1.  
 
-->mode(-1)
Current date is 23-Jun-2013 
 
Welcome to the Textbook Companionship Project 2013 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 Book Title                             :       UNIX CONCEPTS AND APPLICATIONS    
 
 Book Edition                         :                                                                           4   
 
 Book Author                          :                                                    Sumitabha Das   
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 Code Author                          :                                                     Pranav Bhat T   
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 Chapter Number                    :                                                                            23   
 
 Chapter Title                         :                              Systems programming I- Files   
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 6    :               Show the method of reversing a file using error handling alternatives 
 
 ****************************************************************   
 
 Answer    :      
 
 INSTRUCTIONS   :    
  
 1.These programs are part of systems programming in Unix and the commands have NO EQUIVALENT IN SCILAB   
  
 2.However if possible some selected programmes have been TRIED TO BE IMPLEMENTED   
 
 3.For most of the programmes whose equivalent is NOT THERE IN SCILAB,only the output has been printed as given in the textbook w 
      ith no interactive input as in the programme below                                                                          
 
 4.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                                                                              
 
 5.The inconvenience is regretted.   
.............Press [ENTER] to continue.....	UNIX SHELL SIMULATOR(DEMO VERSION WITH PRELOADED COMMANDS)




$ cat reverse_read2.c      # to open the file emp.lst /* Program: reverse_read2.c -- Reads a file in reverse - uses error handling */

#include <fcntl.h>             /* For 0_RDONLY   */
#include <unistd.h>            /* For STDOUT_FILENO */
#include <errno.h>             /* For ENOENT, errno, etc. */
#include <stdio.h>             /* For ENOENT, errno, etc. */

int main(int argc, chr **argv) {
    int size, fd;
    char buf;                  /* Single-character buffer */
    char *mesg = "Not enough arguments\n" ;
   
    if (argc != 2) {           /* Our own user-defined error message */
        write(STDERR_FILENO, mesg, strlen(mesg)); /* Crude form of error*/
        exit(1);                                  /*handling using write*/
    }                                             /* Use fprintf instead*/
    
    if ((fd = open(argv[1],O_RDONLY)) == -1) {
        if (errno == ENOENT) {             /* Checking for specific error*/
            fprintf(stderr, "%s\n",stderror(errno)); /*perror is better*/
            exit(2);
        } else {
           perror(argv[1]);                /* Using two library functions */
           exit(3);                         /* perror and exit.often the  */
        }                                    /* preferred way */
    }                 
    
    lseek(fd, 1, SEEK_END);              /* Pointer taken to EOF + 1 first */
    while (lseek(fd, -2, SEEK_CUR) >=0) { /* and then back by two bytes */    
        if (read(fd, &buf, 1) != 1) {     /* A signal can create error here */
           perror("read");
           exit(4);
        }
        if (write(STDOUT_FILENO, &buf, 1) != 1) { /* Disk may run out of space */
           perror("write");
           exit(5);
        }
   }
   close(fd);               /*Can have error here too*/
    exit(0);                 /* exit doesn't return - hence no error */
}

$ ls   
  ans  =
 
!vv.txt           !
!                 !
!reverse_read2.c  !
!                 !
!Result6.txt      !
!                 !
!Example9.sci     !
!                 !
!Example8.sci     !
!                 !
!Example7.sci     !
!                 !
!Example6.sci     !
!                 !
!Example2.sci     !
!                 !
!Example13.sci    !
!                 !
!Example12.sci    !
!                 !
!Example11.sci    !
!                 !
!Example10.sci    !
!                 !
!ex9              !
!                 !
!ex8              !
!                 !
!ex7              !
!                 !
!ex6              !
!                 !
!ex5              !
!                 !
!ex4              !
!                 !
!ex3              !
!                 !
!ex2              !
!                 !
!ex13             !
!                 !
!ex12             !
!                 !
!ex11             !
!                 !
!ex10             !
!                 !
!ex1              !

$ cat vv.txt     hi there
How are you
I am fine 
Thank You
Good Bye
$ cc reverse_read2.c$ a.out  vv.txt   
......a blank line...           The terminating \n of the last lineeyB dooG

uoY knahT

 enif ma I

uoy era woH

ereht ih 


$ 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)