test.c

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

void tst_error()
{
    char error_message[30] = "An error has occurred\n";
    write(STDERR_FILENO, error_message, strlen(error_message)); 
    exit(1);
}

int changeDir(char** comand)
{
    char* cdCommand = "cd";
    if(strcmp(comand[0], cdCommand) == 0) 
    {
        if(comand[1] != NULL && comand[2] == NULL && access(comand[1], R_OK)==0)
        {
            chdir(comand[1]); 
            return 1;
        }
        if(comand[2] != NULL || comand[1] == NULL)
        {
            printf("Only accept one argument.\n");
        }
        else if(access(comand[1], R_OK)!=0)
        {
            printf("Directory not found : %s\n", comand[1]);
        }
    }
    return 0;
}

//Function to print current directory
void printPrompt()
{
    char dir[1024];
    getcwd(dir, sizeof(dir));
    printf("\033[01;33m"); //change color
    printf("%s", dir);  //print current dir path
    printf("\033[0m"); //reset color
    printf(" >> ");
}



char ** tst_path(char *a[])
{
    int size = 1;
    int bcount = 0;
    char **b = malloc(sizeof(char*));

    while(a[size] != NULL)
    {
        b[bcount] = malloc(strlen(a[size])+1);
        strcpy(b[bcount], a[size]);
        bcount++;
        size++;
    }
    b[bcount] = NULL;
    return b; //should return char** which is array of strings
}

char** split(char* orig, char* delim, int* counter){
    char **arr = malloc(sizeof(char*));
    char *tok = strtok(orig, delim); //parse arguments
    int currindex = 0;

    //traverse token 
    while(tok != NULL){
        arr[currindex] = tok;
        // printf("%d - arg %d: %s\n", getpid(), currindex, argTok);
        currindex++;
        arr = realloc(arr, (currindex+1) * sizeof(char*));
        tok = strtok(NULL, delim);
    }
    
    arr[currindex] = NULL;
    if (counter != NULL)
        *counter = currindex;
    return arr;
}

char* removeSpaces(char* s)
{
    char* cpy = s;  // an alias to iterate through s without moving s
    char* temp = s;

    while (*cpy)
    {
        if (*cpy != ' ' && *cpy != '\t')
            *temp++ = *cpy;
        cpy++;
    }
    *temp = 0;

    //printf("wo white space :%s\n", s); // This prints out the desired result: abbcccd
    return s;
}

/*
free each element in array that is dynamically allocated
*/
void freeArr(char** s){
    for(int i = 0; s[i] != NULL; i++){
        free(s[i]);
    }
    free(s);
}


int
main(int argc, char *argv[])
{
    char *line = NULL;
    size_t len = 0;
    ssize_t nread;
    FILE* input; //input source

    char **paths  = malloc(2 * sizeof(char*));

    //default paths
    paths[0] = strdup("/bin");
    paths[1] = NULL;

    //check if batch file exists
    if(argv[1] != NULL){

        if(access(argv[1], R_OK) == 0){
            input = fopen(argv[1], "r");
        } else {
            tst_error(); //error if path invalid
            free(paths);
            exit(0);
        }

    } else{
        input = stdin;
        printPrompt();
    }

    while ((nread = getline(&line, &len, input)) != -1) {
        //exit
        if(strcmp(line, "exit\n") == 0){
           exit(EXIT_SUCCESS);
        }

        int commandCount; //number of commands
        char **commandArr = split(line, "&\n", &commandCount); //create array of commands
        int procressCount = 0; //number of processes called

        
        //traverse array of commands
        for(int i = 0; i < commandCount; i++){
            int redirCount = 0;
            //parse redirection
            char **redir = split(commandArr[procressCount], ">", &redirCount); 

            if(redirCount > 2){
                tst_error();
                free(redir);
                continue;
            }

            int argCount = 0; // arg count in command
            char **arg = split(redir[0], " :\t", &argCount); //create array of arg
            int child = -1;
            //printf("%s", arg[0]);

            if (arg[0] != NULL){
            
                if(strcmp(arg[0], "cd") == 0){
                    changeDir(arg);     //change directory                
                } 
                else if(strcmp(arg[0], "path") == 0){
                    freeArr(paths);
                    paths = tst_path(arg);   // change path
                    printf("Paths changed");
                } 
                else{
                     child = fork();
                }
            }

            //child procress
            if(child == 0){
                int ofileCount = 0;
                if(redirCount == 2){
                    char ** output = split(redir[1], " \t", &ofileCount);
                    close(STDOUT_FILENO);
                    if(ofileCount == 1)
                        open(output[0], O_CREAT|O_WRONLY|O_TRUNC, S_IRWXU);
                }
               
                if(strcmp(arg[0], "exit") == 0 || ofileCount > 1){
                    tst_error();
                }
                //exec
                else{
                    char* wholename = NULL;
                    int i;

                    //traverse array of paths
                    for(i = 0; paths[i] != NULL; i++){

                        wholename = malloc(sizeof(paths[i]) + sizeof(arg[0]) + 2);
                        strcpy(wholename, paths[i]);
                        strcat(wholename,"/");
                        strcat(wholename, arg[0]);

                        if (access(wholename, X_OK) == 0){ //check if execeutable
                            execv(wholename,arg);   //run
                            free(wholename);
                            break;
                        }
                    }
                    free(wholename);
                    if(paths[i] == NULL){
                        printf("command not found\n");
                    }
                } 
            }
            else{
                procressCount++; //increment no. of process called
            }
            free(arg);
            free(redir);

            if(child == 0)
                exit(0);
        }

        for(int i=0; i < commandCount; i++){
            wait(NULL);
        }
        free(commandArr);
        if(input == stdin){
            printPrompt();
        }
    }

    freeArr(paths);
    free(line);
    exit(EXIT_SUCCESS);
}