Question

Design and implement a simple, interactive shell program that prompt the user for a command, parser the command (you do not need to write a parser) and then execute it. The commands are:

1. attrib file.

To make the file read only.

2. copy fileA fileB

To copy fileA into fileB.

3. delete file

To delete the file.

4. dir name or just dir

The listing of the directory name is displayed. In case of just dir, the list of the      items in the current directory should show up.

5. exec Name

The shell should execute the class Name.class. The java file Name.java is the main method (i.e. the method main is declared in this class).

6. mkdir name

Makes a directory named name.

7. date

Displays the current date.

8. time

Displays the current time.

9. edit

displays the Notepad editor on the screen.

10. rename fileA fileB

Renames  fileA to fileB.

11. rmdir name

Removes the directory named name.

Answer 1

int main(int argc, char **argv)
{
// Load config files, if any.

// Run command loop.
lsh_loop();

// Perform any shutdown/cleanup.

return EXIT_SUCCESS;
}
void lsh_loop(void)
{
char *line;
char **args;
int status;

do {
printf("> ");
line = lsh_read_line();
args = lsh_split_line(line);
status = lsh_execute(args);

free(line);
free(args);
} while (status);
}

#define LSH_RL_BUFSIZE 1024
char *lsh_read_line(void)
{
int bufsize = LSH_RL_BUFSIZE;
int position = 0;
char *buffer = malloc(sizeof(char) * bufsize);
int c;

if (!buffer) {
fprintf(stderr, "lsh: allocation error\n");
exit(EXIT_FAILURE);
}

while (1) {
// Read a character
c = getchar();

// If we hit EOF, replace it with a null character and return.
if (c == EOF || c == '\n') {
buffer[position] = '\0';
return buffer;
} else {
buffer[position] = c;
}
position++;

// If we have exceeded the buffer, reallocate.
if (position >= bufsize) {
bufsize += LSH_RL_BUFSIZE;
buffer = realloc(buffer, bufsize);
if (!buffer) {
fprintf(stderr, "lsh: allocation error\n");
exit(EXIT_FAILURE);
}
}
}
}

char *lsh_read_line(void)
{
char *line = NULL;
ssize_t bufsize = 0; // have getline allocate a buffer for us
getline(&line, &bufsize, stdin);
return line;
}
to do some of the dirty work for us.

#define LSH_TOK_BUFSIZE 64
#define LSH_TOK_DELIM " \t\r\n\a"
char **lsh_split_line(char *line)
{
int bufsize = LSH_TOK_BUFSIZE, position = 0;
char **tokens = malloc(bufsize * sizeof(char*));
char *token;

if (!tokens) {
fprintf(stderr, "lsh: allocation error\n");
exit(EXIT_FAILURE);
}

token = strtok(line, LSH_TOK_DELIM);
while (token != NULL) {
tokens[position] = token;
position++;

if (position >= bufsize) {
bufsize += LSH_TOK_BUFSIZE;
tokens = realloc(tokens, bufsize * sizeof(char*));
if (!tokens) {
fprintf(stderr, "lsh: allocation error\n");
exit(EXIT_FAILURE);
}
}

token = strtok(NULL, LSH_TOK_DELIM);
}
tokens[position] = NULL;
return tokens;
}

int lsh_launch(char **args)
{
pid_t pid, wpid;
int status;

pid = fork();
if (pid == 0) {
// Child process
if (execvp(args[0], args) == -1) {
perror("lsh");
}
exit(EXIT_FAILURE);
} else if (pid < 0) {
// Error forking
perror("lsh");
} else {
// Parent process
do {
wpid = waitpid(pid, &status, WUNTRACED);
} while (!WIFEXITED(status) && !WIFSIGNALED(status));
}

return 1;
}

/*
Function Declarations for builtin shell commands:
*/
int lsh_cd(char **args);
int lsh_help(char **args);
int lsh_exit(char **args);

/*
List of builtin commands, followed by their corresponding functions.
*/
char *builtin_str[] = {
"cd",
"help",
"exit"
};

int (*builtin_func[]) (char **) = {
&lsh_cd,
&lsh_help,
&lsh_exit
};

int lsh_num_builtins() {
return sizeof(builtin_str) / sizeof(char *);
}

/*
Builtin function implementations.
*/
int lsh_cd(char **args)
{
if (args[1] == NULL) {
fprintf(stderr, "lsh: expected argument to \"cd\"\n");
} else {
if (chdir(args[1]) != 0) {
perror("lsh");
}
}
return 1;
}

int lsh_help(char **args)
{
int i;
printf("Stephen Brennan's LSH\n");
printf("Type program names and arguments, and hit enter.\n");
printf("The following are built in:\n");

for (i = 0; i < lsh_num_builtins(); i++) {
printf(" %s\n", builtin_str[i]);
}

printf("Use the man command for information on other programs.\n");
return 1;
}

int lsh_exit(char **args)
{
return 0;
}

int lsh_execute(char **args)
{
int i;

if (args[0] == NULL) {
// An empty command was entered.
return 1;
}

for (i = 0; i < lsh_num_builtins(); i++) {
if (strcmp(args[0], builtin_str[i]) == 0) {
return (*builtin_func[i])(args);
}
}

return lsh_launch(args);
}