minsh/minsh.c

/*
 * =====================================================================================
 *
 *       Filename:  minsh.c
 *
 *    Description:  A simple shell
 *
 *        Version:  1.8.6
 *        Created:  08/31/2017 03:14:02 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  David Muckle, 
 *   Organization:  
 *
 * =====================================================================================
 */
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <dirent.h>
#include "hashmap.h"
#include <pwd.h>
#include <sys/types.h>
typedef int bool;
#define true 1
#define false 0
char* user;
char host[32];
bool verbose = false;
char homedir[64];
char* aliascommands[256];
char* aliasnames[256];
int aliascount = 0;
int alias(char* aliasname, char* aliascommand){
	strcpy(aliasname, aliasnames[aliascount]);
	strcpy(aliascommand, aliascommands[aliascount]);
	aliascount++;
	return 0;
}
int main(int argc, char** argv)
{
	//Help stuff and verbose mode
	int should_run = 1;
	for(int i = 0; i < argc; i++){
		if(strcmp(argv[i], "-v") != 0 && strcmp(argv[i], "--help") != 0 && i>=1){
			fprintf(stderr, "Invalid flag, use --help for more information\n");
			exit(1);
		}
		if(strcmp(argv[i], "-v") == 0){
			verbose = true;
			printf("Running in verbose mode\n");
		}
		if(strcmp(argv[i], "--help") == 0) {
			printf("Minsh - a simple shell\n-v - Start in verbose mode\nMinsh is a simple shell that supports commands and stdout redirection\n");
			exit(0);
		}
	}
	if(verbose){
		printf("Getting user and hostname for custom prompt\n");
	}
	struct passwd *userinfo = getpwuid(getuid());
	user = userinfo->pw_name;
	gethostname(host, 32);
	sprintf(homedir, "/home/%s", user);
	char dir[128];
	while (should_run){
	        getcwd(dir, 128);	
		printf("%s@%s:%s> ", user, host, dir);
		fflush(stdout);
		char command[256];
		//Actuall take the command input. Since we have to give fgets a buffer, this determines our command string size too
		if(fgets(command, 256, stdin) == NULL){
			//If we were just piped input, don't loop on the input, just run whatever command was fed
			printf("\n");
			break;
		}
		//If user only hit return, skip all this and just loop back
		if(strcmp(command, "\n") == 0){
			continue;
		}
		//Remove the newline at the tail of the command
		strtok(command, "\n");
		//Exit if we need to
		if(strcmp(command, "exit") == 0){
			if(verbose){
				printf("Alright, we're exiting\n");
			}
			exit(0);
		}
		//Chop up the command into the command itself and the arguments
		char *cmdArgs[256];
		char initialCommand[256];
		//Preserve our initial command so we can print it out later if verbose, or if the command is invalid
		strcpy(initialCommand, command);
		//Start putting flags into cmdArgs
		//Running strtok with an arg of NULL just picks up where the last strtok left off
		//This also gives us a nifty value in i, the length of the array of args
		//We don't have to set the last value to NULL for execvp since strtok does that when it can't find any more strings
		int i=0;
		cmdArgs[i] = strtok(command, " ");
		while(cmdArgs[i] != NULL){
			cmdArgs[++i] = strtok(NULL, " ");
		}
		//Check if we just want to cd
		if(strcmp(command, "cd") == 0){
			if(i == 1){
				if(verbose){
					printf("No directory supplied, changing to \"%s\n\"", homedir);
				}
				chdir(homedir);
				continue;
			} else {
				if(chdir(cmdArgs[1]) == 0){
					if(verbose){
						printf("Changing directory to \"%s\"\n", cmdArgs[1]);
					}
				}else{
					printf("Error: no such file or directory\n");
				}
				continue;
			}
		}
		//Perform the actual command
		int rc = fork();
		if(rc<0){
			perror("fork");
			exit(1);
		}
		else if(rc == 0){
			//Check if we're redirecting to a file
			//We have to check if i is greater than one, because the next conditional subtracts 2 from i
			//If i isn't greater than one, we get a bad array access and our command just doesn't run
			if(i > 1){
				if(strcmp(cmdArgs[i-2], ">") == 0){
					if(verbose){
						printf("Fork with redirect successful, running \"%s\" with pid %d\n", initialCommand, (int) getpid());
					}
					close(STDOUT_FILENO);
					open(cmdArgs[i-1], O_CREAT|O_WRONLY|O_TRUNC, 0644);
					//Set where our > was so execvp won't read past it
					cmdArgs[i-2]=NULL;
					execvp(command, cmdArgs);
					//Execvp will only return if it fails to run a command, thus...
					fprintf(stderr, "Command \"%s\" not found...\n", initialCommand);
					exit(1);
				}
			}
			if(verbose){
				printf("Fork successful, running \"%s\" with pid %d\n", initialCommand, (int) getpid());
			}
			execvp(command, cmdArgs);
			//Execvp will only return if it fails to run a command, thus...
			fprintf(stderr, "Command \"%s\" not found...\n", initialCommand);
			exit(1);
		}
		else{
			wait(NULL);
			if(verbose){
				printf("Child process %d (parent pid: %d) done waiting\n", rc, (int) getpid());
			}
		}
	} 

	return 0;
}