Piping commands with redirection

[opt!kal]

Homework Statement

Hi there,

So I am working on this assignment where the user is supposed to input a variety of UNIX commands and they must behave as if one typed it into the terminal. My current problem lies with when a user tries to redirect the inputted commands to some file. Currently it only works when a user has the redirect symbol, like:

ls -l | sort -n > temp.txt

However if I try to input:
ls -l | sort -n

I just segfault. I know the problem most likely lies in how I wrote the redirect option, but I can't seem to figure out how to make it so that the two above commands work.

The Attempt at a Solution

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

/*get args function*/

#define MAXARGS 256
char ** getargs(char * cmd) {
	// assumes that cmd ends with NULL
	char** argsarray;
	int nargs = 0;
	int nlen = strlen(cmd);
	int i = 0;
	argsarray = (char**) malloc(sizeof(char*) * MAXARGS);
	argsarray[0] = strtok(cmd," ");
	i = 0;
	while (argsarray[i] != NULL){
		i++;
		argsarray[i] = strtok(NULL," ");
	}
	return argsarray;
}int main(void){

  pid_t childpid;
  int fd[256][2];
  char cmd[256];
  char * sepCmd[256];
  char * pch;
  char * srch;

  printf("Please enter a command sequence: \n");
  gets(cmd);
  //scanf("%s", cmd);
  printf("You have entered: %s \n", cmd);
  

  printf("Attempting to split up command: \n");
  pch = strtok (cmd, "|");
  
  srch = strchr(cmd, '>');
  *srch++ = '\0'
  while (*srch == ' ') ++srch;

  int count = 0;  
    while (pch != NULL && count < 256) {
      printf("%s\n", pch);
      sepCmd[count] = pch;
      printf("The value in this array value is: %s\n", sepCmd[count]);
      pch = strtok (NULL, "|");
      count++;
  }
  
  char ** argue;
  int k;
  
  /* Block that deals with the first command given by the user */
  k = 0;
  pipe(fd[k]);
  if(!fork()) {
	  	dup2(fd[k][1], STDOUT_FILENO);
		close(fd[k][0]);
		argue = getargs(sepCmd[k]);
		execvp(argue[0], argue);
		perror(argue[0]);
		exit(0);
  }

  /*Loop that will control all other comands except the last*/
  for(k = 1; k <= count - 2; k++) {
	  close(fd[k-1][1]);
	  pipe(fd[k]);
	  
	  if(!fork()) {
		  close(fd[k][0]);
		  dup2(fd[k-1][0], STDIN_FILENO);
		  dup2(fd[k][1], STDOUT_FILENO);
		  argue = getargs(sepCmd[k]);
		  execvp(argue[0], argue);
		  perror(argue[0]);
		  exit(0);
	  }
  }
  
  
  /*Block that will take care of the last command in the sequence*/
  k = count - 1;
  
  close(fd[k-1][1]);
  if(!fork()) {
	  dup2(fd[k-1][0], STDIN_FILENO);
	  argue = getargs(sepCmd[k]);
          if (srch) dup2(open(srch, O_RDWR|O_CREAT), STDOUT_FILENO);
	  execvp(argue[0], argue);
	  perror(argue[0]);
	  exit(0);
  }
  while(waitpid(-1, NULL, 0) != -1);
}

Any help is greatly appreciated

 

[opt!kal]

So a little update,

I changed gets to fgets and it seems like it will take any amount of comannds piped together, but only if it ends with a redirection operator or else I get errors like:

<COMMAND>: invalid option -- '

where COMMAND is the last command in the sequence

 

[Mene]

.It seems like the issue lies in properly handling the redirect symbol in your code. It's important to make sure that the file descriptor for the output file is properly set and that any necessary file permissions are being taken into account. It may also be helpful to use the dup2() function to redirect the output to the file before executing the command, rather than trying to do it after the command has already been executed. Additionally, it may be helpful to use the perror() function to get more detailed information about any errors that are occurring. I would suggest reviewing your code and making sure that all necessary steps are being taken to properly handle the redirection of output.