Programming

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/* The following define's belongs to read_command(..) */
#define MAXPARMS	20
#define MAXPARMLEN	255
#define MAXINPUT	255
#define shell		"cesh"

/* The Command line parser */

/*------------------------------------------------------------------*/
/* read_command:                                                    */
/*   Print the prompt and get one characters from the users which   */
/*   makes up an entire command line entry                          */
/*------------------------------------------------------------------*/

void read_command(char * command, char * parameters[])
{
  char input[MAXINPUT];
  char * parm;
  char c;
  int i;

  /* initialize the whole parameters array to NULL pointers */
  for (i=0;i<MAXPARMS;i++)
    {
      parameters[i]=NULL;
    }

  i=0;
  input[0]='\0';

  /* loop until some characters are entered on the command line */
  do
    {
      printf("%s> ", shell);
      c=getchar();
      while ((c != '\n') && (i < MAXINPUT-1))
        {
          input[i]=c;
          i++;
          c=getchar();
        }
      input[i]='\0';
    } while (strlen(input)==0);

  /* copy the first "word" on the command line into the command var */
  /* this also initializes the use of the strtok function */
  strcpy(command, strtok(input, " "));
  parameters[0]=malloc((MAXPARMLEN+1)*sizeof(char));
  strcpy(parameters[0], command);
  i=1;

  /* separate all of the "words" on the command line. Each becomes */
  /* a string pointed to by the parameters array using strtok. */
  do
    {
      if (parm=strtok(NULL, " "))
        {
          parameters[i]=malloc((MAXPARMLEN+1)*sizeof(char));
          strcpy(parameters[i],parm);
        }
      else
        {
          parameters[i]=NULL;
        }
      i++;
    } while((parameters[i-1]!=NULL) && (i < MAXPARMS));

  return;
}

int main(void)
{
char name[10];
char *argv[MAXPARMS];

read_command(name, argv);

/*background process*/
int pid, status;
int BGRND = 0;

do 
{
	if (strcmp(argv[0], "&")==0))
	{
		BGRND = 1;
	}
	if ( (pid = fork() < 0 )
			return 0;

	if(pid == 0 )
	{
		if ((execvp(argv[0], argv)) == -1)
			printf("%s: Command not found.\n", tokenstr);
			return 0;
	}
	if(BGRND == 0)
	{
		while (waitpid(-1, &status, 0) != pid);
	}
	BGRND = 0;
}while(strcmp(name,"exit));

return 0;
}

if ( (pid=fork()) == -1 ) {
         fprintf(stderr, "fork failed \n");
         fprintf(stderr, "errno = %d \n", errno);
         fprintf(stderr, "%s\n", sys_errlist[errno]);
         exit(1);
}