Bash Shell doesn't work as expected - Arguments to the execvp( ) are not accepted

[david687]

I'm building a shell for bash in C , and I try to execute simple commands , but the output of the shell is not correct .

As for the moment it only supports the > feature , e.g writing to a file the output of the running program .

The code : main() code

	char errorStr[BUFF3];
	 while (1)
	 {

		 int i , errorFile , fd;
		 char ch;

	     char *line = malloc(BUFFER);
	     char *origLine = line;
	     // fgets(line, BUFFER, stdin);   // get a line from stdin . ls Debug > t.ourr
	     scanf("%[^\n]",line);            // ls Debug > dir.out
	     scanf("%c",&ch);

	     // get complete diagnostics on the given string

	     lineData info = runDiagnostics(line);

	     char command[20];
	     sscanf(line, "%20s ", command);

	     printf("The Command is: %s\n", command);

	     int currentCount = 0;					// number of elements in the line
	     int *argumentsCount = &currentCount;   // pointer to that


	     // get the elements separated

	     char** arguments = separateLineGetElements(line,argumentsCount);


	     executeCommand(info , line , arguments , argumentsCount);

And auxiliary methods :

void runGreaterThan(char* command , char** arguments , int numberOfArguments)
{
	int i = 0 ;
	int errorFile = 0, fd;
	char errorStr[BUFF3];

	char * fileName = arguments[numberOfArguments - 1];

	fd = open(fileName,O_WRONLY | O_TRUNC | O_CREAT,0600);
    if (fd < 0)
    {
         perror("open failed\n");
         exit(0);
    }


    pid_t pid ;

    if (-1 == (pid = fork()))         // fork failed
    {
		sprintf(errorStr,"fork: %s\n",strerror(errno));
		write(errorFile,errorStr,strlen(errorStr + 1));
		perror("fork");
		exit(1);
    }


    else if (0 == pid)  			// fork was successful
    {
		printf("\nIn son process\n");
		dup2(fd, STDOUT_FILENO);
		close(fd);

		if (execvp(command,arguments)  < 0)       // execute the command
		{
			perror("execvp");
			printf("ERROR: execvp failed\n");
			exit(1);
		}

    }

    else // parent
    {
 	    int status = 0;
		pid = wait(&status);
		printf("Process %d returned with status %d.\n", pid, status);
    }


}

and

void executeCommand(lineData info , char* wholeLine , char ** arguments , int * argumentsCount)
{

	int totalPipes = info.numberPipes;  // use this for knowing how much pipes we'd have
	int i = 0 , j = 0;         // use this to run on the whole string
	char* command = NULL;  // here we store the command

	char ** args = (char**)malloc(4 * sizeof(char*));  // create 4 cell for now

	int iterator = 0;   // using this to iterate the separated arguments


	// running on all the line , even if we have 0 zero pipes

	int currectCommandCount = 0;

	while (iterator <= totalPipes)
	{
		int argCount = *argumentsCount;
		while (i < argCount && (strcmp(arguments[i], "|\0") != 0) )
			{
				if (i == 0)
					command = arguments[i];
				else if (strcmp(arguments[i] , ">\0") != 0)   // meaning - don't put the > sign in the arguments
				{
					currectCommandCount++;
					args[j] = (char*) malloc(strlen(arguments[i]) * sizeof(char));
					strcpy (args[j] , arguments[i]);
					j++;
				}

				i++;
			}

		// here we execute the current command & its args & its counter of args


		runGreaterThan(command , args , currectCommandCount);

		iterator++;
	}

}

The problem : when I execute the command ls Debug/ > q.out all I get is a the file with its name appearing in it ,
but without the contents of the folder Debug .
I suspect that there is something wrong with my execvp() function .

Any idea how to fix this ? I've tried to make this work for the past two days ,but nothing .

Update : Eclipse thinks that for ls > r.out , the > is a library (folder) , so I get
as the output : cannot access >: No such file or directory . How can I fix this ?


Best Regards
David

[Catfish]

Update : Eclipse thinks that for ls > r.out , the > is a library (folder) , so I get
as the output : cannot access >: No such file or directory . How can I fix this ?

Do you by mistake feed the ">" to ls as an argument?

Little parts of your code are weird: e.g. strcmp(arguments[i], "|\0")
You must know that the '\0' gets added automatically when you declare a string literal.
So your actual C string in that example has a size of 3 and looks like |\0\0 in memory.

You also don't seem to free() what you malloc(), potentially leading to memory leaks.

I'm sorry I cannot help you more; but as an advice: always strive for simplicity in design, because languages like C and C++ tend to add the complexity in implementation themselves.

Edit: code tags.

[david687]

My friend , the thing is that the > is supposed to be one of the arguments for execvp , then
of course I added that . But Eclipse doesn't treat that as an argument , but as a folder ! and this , is a mistake that I can't seem to understand why ...thanks 4 the help !