gistfile1.c

/*
 * sh1.c: sample version 1 of a UNIX command shell/interpreter.
 * Stefan Brandle, COS 421, Feb 2000. Mod Feb 2001.
 */

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

//prototypes

//parse a command into array of arguments
//arg[0] command 
//arg[1--(n-1)] arguments
//arg[n] NULL

void parsecmd(char*, char**); //parse command into array of arguments
void exec(char**); //run command

int main()
{
    char line[256];
    char prompt[] = "grsh$";
    char * argv[64]; //cmd line arguments
    /* spit out the prompt */
    printf("%s", prompt );

    
    /* Try getting input. If error or EOF, exit */
    while( fgets(line, sizeof line, stdin) != NULL )
    {

		/* fgets leaves '\n' in input buffer. ditch it */
		line[strlen(line)-1] = '\0';

		/* This is where I take the easy route.
			system(line);
		   fork(), execvp() & co. go here in your version*/

		//printf("%s", prompt);
		
		parsecmd(line, argv);

		if (strcmp(*argv,"list") == 0)
			*argv = "ls"; //change first argument to ls command
		else if (strcmp(*argv,"exit") == 0 )
			exit(0);

    exec(argv);

    printf("%s",prompt);

	
    }
    
    return 0;
}
//taken from csl.mtu.edu
void parsecmd(char *line, char **argv)
{
	while (*line != '\0')  /* if not the end of line ....... */ 
  {      
          
          while (*line == ' ' || *line == '\t' || *line == '\n')
               *line++ = '\0';     /* replace white spaces with 0    */
          
          *argv++ = line;          /* save the argument position     */
          
          while (*line != '\0' && *line != ' ' && 
                 *line != '\t' && *line != '\n') 
               line++;             /* skip the argument until ...    */
  }
  
  *argv = '\0';                 /* mark the end of argument list  */	
}

void exec(char** argv)
{
  
  int pid = fork();
  if (pid == 0 ) //child process
  {
    execvp(*argv, argv);
  }


}