cshell/main.c

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

#define	true	1
#define	false	0
#define LEN 512
#define PATH "/bin/"
#define ERROR -1
#define EXIT_1 256

int getHostName(char* host);
int getUserName(char* name);
int runExec(char** args, int writeToFile);
void PrintTokens (char** tokens);
char** ReadTokens(FILE* stream, int* writeToFile) ;
void FreeTokens(char** tokens) ;
void checkIfQuit(char* word);
int getFileNameIndex(char** args);
void freeRemainderInArr(char** args, int beforLast);



int main()
{
	int exitCode = 0;
	char* host_n = (char *)malloc(sizeof(char));
	char* user_n = (char *)malloc(sizeof(char));
	char** args;
	int writeToFile = false;
	
	if(getHostName(host_n) == ERROR)
		goto quit;
	if(getUserName(user_n) == ERROR)
		goto quit;

	signal(SIGINT, SIG_IGN); // ignore SIGINT

	while(1)
	{
		printf("%d %s@%s$ ",exitCode, user_n, host_n); // Print Prompt
		args = ReadTokens(stdin, &writeToFile); // get user command and tokenize it to args, check if there is a redirect to file.
		if(args != NULL) // if user did enter a command do the following
		{
			exitCode = runExec(args, writeToFile); // fork and run the process, return child exit code
			FreeTokens(args); //in case of error while trying to create process - this method will free the memory already
			if(exitCode == ERROR) // in case we need to exit.
				goto quit;
		}
		writeToFile = false; // set the "boolean" back to default
	}

	quit:
	free(host_n);
	free(user_n);
	return 0;
}

/**
 * Atemting to get the host name from the system
 * @param  host  - the string that will hold the host name
 * @return      0 if all went well, -1 (ERROR) otherwise 
 */
 int getHostName(char* host)
 {
 	if(gethostname(host, 10) != 0)
 	{
 		fprintf(stderr, "%s\n", "Error: while getting host name");
 		return ERROR;
 	}
 	return 0;
 }

/**
 * Atemting to get the user name from the system
 * @param  host  - the string that will hold the user name
 * @return      0 if all went well, -1 (ERROR) otherwise 
 */
 int getUserName(char* name)
 {
 	if(getlogin_r(name, 10) != 0)
 	{
 		fprintf(stderr, "%s\n", "Error: while getting User name");
 		return ERROR;
 	}
 	return 0;
 }

/**
 * This function will atempt to create a new Process.
 * and will return the exit status code of the child
 * @param  args - an array of strings that contains all the arguments from the user
 * @return  int - exit status of child
 */
 int runExec(char** args, int writeToFile)
 {
 	int status;
 	pid_t pid;
 	char* path = (char *)malloc(sizeof(char));  
 	char* exe = (char *)malloc(sizeof(char));
 	strcpy(exe,args[0]);
 	strcpy(path, PATH);
 	strcat(path, exe);

 	pid = fork();

 	if(pid < 0)
 	{
 		fprintf(stderr, "%s\n", "Error: Could not create a new process");
 		return ERROR;
 	}
	else if(pid == 0) // child
	{
		signal(SIGINT, SIG_DFL); // set the child SIGINT handler to default! -> ^C will kill child but not father.
		
		if(writeToFile == true)
		{
			int i_lastArg = getFileNameIndex(args);
			char* fileName = (char *)malloc(strlen(args[i_lastArg])*sizeof(char));
			strcpy(fileName, args[i_lastArg]); //saving file name before cleaning the array
			freeRemainderInArr(args, i_lastArg);
			
			int fd = open(fileName, O_RDWR | O_CREAT | O_TRUNC);
			if(fd >= 0)
			{
				dup2(fd, 1);   // make stdout go to file
				close(fd);
			}
			else
			{
				fprintf(stderr, "%s%s%s\n", "Unable to open file ",fileName," : printing out put to default stdout:");
			}


		}


		if(execv(path, args) != 0)
		{
			fprintf(stderr, "%s%s%s\n", "cshell: ", args[0] ,": command not found");
			exit(1); //child error - chield needs to be closed manually. exit code 225;
		}
	}
	else //pid > 0 father
		waitpid(pid,&status,0);

	free(path);
	free(exe);
	if(status == EXIT_1) //in my computer exit(1) returns 256 - ex demands wanted 255
		return status-1;
	return status;
}

/**
 * this func will read a full line and will store all the arguments in an array (of char*).
 * if the line will have only 1 word - it will call afunction to check if the word is "quit".
 * 
 * @param  stream FILE* - in our case stdin
 * @return        if all went well , an Array of arguements from the input line.
 */
 char** ReadTokens(FILE* stream, int* writeToFile)
 {
 	char** returnArr;
	char input[LEN]; // the var to hold the line
	char temp[LEN]; // will be a copy of the input line - so we can figure how many words we have
	int wordCnt = 0; // word counter
	int i = 0; //index for second iteration
	fgets(input, LEN, stream); // get the linei

	strcpy(temp, input); // copy the line
	
	//strkot first iteration to count words (corrups temp var)
	char* tok;
	tok = strtok(temp," \n");
	while (tok != NULL)
	{
		wordCnt++;
		tok = strtok(NULL, " \n");
	}

	if(wordCnt == 0) //if there are no "words" in input - return null
		return NULL;
	

	returnArr = (char**)malloc((wordCnt + 1)*sizeof(char*)); //allocates the memory for the array
	if(returnArr == NULL)	//check if the malloc func finished successfuly 
	{
		fprintf(stderr,"%s\n", "ERROR: unable to allocate memory.");
		exit(1);
	}

	//strtok second iteration - puts all words in an index of the array
	tok = strtok(input," \n");
	while (tok != NULL)
	{
		returnArr[i] = (char *)malloc(strlen(tok)*sizeof(char));
		strcpy(returnArr[i], tok);
		if(wordCnt == 1)
			checkIfQuit(tok);
		if(i == wordCnt-2) // one before the last argument. to see if to put output into file.
			if(strcmp(">", returnArr[i]) == 0)
				*writeToFile = true;
			tok = strtok(NULL, " \n");
			i++;
		}

	returnArr[wordCnt] = NULL; // the last index will be NULL - so we know where the end is.
	return returnArr;
}

/**
 * if there is only one word in the input nile the ReadTokens func will call this func.
 * it will check if user want to exit our program
 * 
 * @param word  - the one word to check
 */
 void checkIfQuit(char* word)
 {
 	if(strcmp(word, "exit") == 0)
 		exit(0);
 }

/**
 * this func will print an array of char*, it will know when to finish if the
 * last index is NULL!
 * @param tokens  -  char* Array
 */
 void PrintTokens (char** tokens)
 {
 	int i;
 	for (i = 0; tokens[i] != NULL; i++)
 	{
 		printf("%s\n", tokens[i]);
 	}
 }

/**
 * this will make sure no memory leeks will occurd.
 * runs through all indexes change them to null and then free them.
 * after that it will fraa the array pinter itself.
 * @param tokens - an array to free
 */
 void FreeTokens(char** tokens) 
 {
 	int i = 0;
	while(tokens[i] != NULL) // free all the indexes except the last one (NULL)
	{
		tokens[i] = NULL;
		free(tokens[i]);
		i++;
	}
	free(tokens[i]); // free the last index
	tokens = NULL; // free the array
	free(tokens);
}

/**
 * returns the index of the File name to redirect output to.
 * @param  args - an array of all the arguments
 * @return int 	- index whare the fileName is in
 */
int getFileNameIndex(char** args)
{
	int i = 0;
	while(args[i] != NULL)
		i++;
	//we are at the end of the array.
	return i-1; //the last arg must be the file name
}

/**
 * this function will modify th args array, in case of redirecting.
 * in that case, the 2 last args are ">" -> "filename"
 * so, the function will put Null insted of ">", and will free
 * the unneeded array cells.
 * @param args      - the array of arguments
 * @param beforLast - the index of ">"
 */
void freeRemainderInArr(char** args, int beforLast)
{
	free(args[beforLast+1]);
	args[beforLast] = NULL;
	free(args[beforLast]);
	args[beforLast - 1] = NULL;
}