Question

Round 1: sequence.c This program should read and execute a list of commands from stdin. Each command and its arguments (if any) will appear on a separate line. For example, if the file "cmdfile" contains the lines: whoami cal 4 2019 echo The time is: date then running 1 /sequence< cmdfile should output your username, a calendar of the month of April, the string "The time is:", and the current date/time, to standard output. Suggested approach: first, make sure you can parse a command and its arguments correctly, and store them as an array of C strings. Test this thoroughly before moving on, making use of trace statements to make sure you've accounted for all the cases you can come up with! Debugging processes and pipes can be tricky so you want to have confidence you are giving later parts of your program the correct input. For the purposes of this prac, you can assume a maximum of 10 arguments per command, 256 characters per line, and 100 lines per file. Second, look at the exec) family of functions and use one to execute each command in turn. Hint: there is a sample program from the first lecture on processes that does something very similar! Here is a pseudo-code version of the setup:

Answer 1

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/wait.h>

#define MAX 100
/*Function definition to parse the command */
void parse(char *line,char **argv){
   while(*line !='\0'){
       while(*line ==' ' || *line == '\t' || *line == '\n')
           *line++ = '\0';
       *argv++ = line;
       while(*line !='\0' && *line != ' ' && *line != '\t' && *line != '\n')
           line++;
   }
   *argv = '\0';
}
/*Function definition of main()*/
int main(int argc, char *argv[]){
   char *arg[MAX],line[256];
   int status;
   pid_t pid;
   FILE *fp;
   /*Error checking for number of command line arguments */
   if(argc < 2){
       printf("Input file is missing!!\n");
       exit(0);
   }
   fp = fopen( argv[1],"r");
   /* Error checking for file opening */
   if(fp == NULL){
       printf("Error in opening file!!\n");
       return 0;
   }

/* Reading file line by line */
   while(fgets(line,256,fp)!= NULL){
       strtok(line, "\n");
       pid = fork();       //creating child process using fork() system call.
       /*Errro checking for creation of child */
       if(pid < 0){
           printf("Forking Failed!!\n");
           exit(1);
       }
       else if(pid == 0){
           parse(line,arg);       //Function call to parse command
           if(execvp(*arg,arg) < 0){
               printf("Execvp failed!!\n");
               exit(1);
           }

       }else{
           wait(&status);       //Waiting for child process to finish.
       }
   }
   return 0;
}

SCREEN SHOTS:

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else wai&sta:iting for chid procoss t o finsh. relurn 0;

Programs$ gcc shell.c :-/Programs$ -la.out :/Programs /a.out cndfile i/Progranss /a.out test Error in opentng file!! Input file is missing!! samsher Su No Tu We Th Fr sa April 2019 7 8 9 10 11 12 13 14 15 16 17 18 19 2e 21 22 23 24 25 26 27 28 29 30 The tine is: Tue Apr 23 21:44:06 IST 2019 /Prograns$