Creating a history function for a Unix Shell - c++

Question

Here is what my program currently looks like. I have to add history functionality that gets stored in a file 'mysh.history'. Currently I expect my output to simply append each user command in my shell to the file.
first line of output
first line of output
It only appends the first input into the shell instance. I think my problem lies with my understanding of the fork() process but I'm not sure what is going on. Any suggestions?
#define MYSH_BUFFERSIZE 64
#define MYSH_DELIM " \t\n"
fstream file;
// custom function declarations
int mysh_exit(char **args);
int mysh_add_history(char **args);
int mysh_history(char **);
char byebye[] = "byebye";
char exit_program[] = "exit";
char history[] = "history";
// contains names of all custom shell commands implemented
char *lookup_str[] = {byebye, exit_program, history};
// holds references to all commands in lookup_str[]
// order or commands must match each other
int (*lookup_func[])(char **) = {
&mysh_exit,
&mysh_exit,
&mysh_history
};
/* custom shell commands implementations BEGIN*/
// Without the argument, it prints out the recently typed commands (with their
// arguments), in reverse order, with numbers
// If the argument “-c” is passed, it clears the list of recently typed commands.
void clear_history()
{
file.close();
file.open("mysh.history", ios::trunc);
}
int mysh_add_history(char *line)
{
// if exists then append to the history
if (access("mysh.history", F_OK) == 0)
{
file.open("mysh.history", ios::app);
}
// otherwise create mysh.history and start writing
else
{
file.open("mysh.history", ios::out);
}
file << line << "\n";
return 0;
}
int mysh_history(char **)
{
return 0;
}
int mysh_exit(char **args)
{
return 0;
}
int num_commands()
{
return sizeof(lookup_str) / sizeof(char *);
}
/* custom shell functions END*/
/* main shell processes BEGIN*/
// returns the tokens (arguments) array after tokenizing line from mysh_read_line()
char **mysh_split_args(char *line)
{
int buffer_size = MYSH_BUFFERSIZE;
int current_pos = 0;
char **tokens = (char **)malloc(buffer_size * sizeof(char *));
char *tok;
if (!tokens)
{
printf("mysh: memory allocation error\n");
exit(EXIT_FAILURE);
}
tok = strtok(line, MYSH_DELIM);
while (tok != NULL)
{
tokens[current_pos] = tok;
current_pos++;
if (current_pos >= buffer_size)
{
buffer_size += MYSH_BUFFERSIZE;
tokens = (char **)realloc(tokens, buffer_size * sizeof(char *));
if (!tokens)
{
printf("mysh: memory allocation error\n");
exit(EXIT_FAILURE);
}
}
tok = strtok(NULL, MYSH_DELIM);
}
tokens[current_pos] = NULL;
return tokens;
}
// mysh_read_line allocates MYSH_BUFFER_SIZE of memory to the intial buffer
// it reallocates memory as needed with getLine() function
// returns line to be processed and tokenized by mysh_split_args()
char *mysh_read_line(void)
{
char *line = NULL;
size_t buffersize = 0;
// getLine() also needs to check for EOF after in the case of text files being read.
if (getline(&line, &buffersize, stdin) == -1)
{
if (feof(stdin))
{
exit(EXIT_SUCCESS);
}
else
{
printf("failed to read line\n");
exit(EXIT_FAILURE);
}
}
return line;
}
// args passed comes from mysh_split_args()
int mysh_launch_process(char **args)
{
pid_t pid;
pid_t wpid;
int state;
pid = fork();
// if we enter child process
if (pid == 0)
{
if (execvp(args[0], args) == -1)
{
printf("error in mysh\n");
}
exit(EXIT_FAILURE);
}
// forking failed
else if (pid < 0)
{
printf("error in mysh\n");
}
else
{
// if we enter parent process
do
{
wpid = waitpid(pid, &state, WUNTRACED);
} while (!WIFEXITED(state) && !WIFSIGNALED(state));
}
return 1;
}
// calls mysh_launch_process() and handles programs being called
int mysh_execute(char **args)
{
int i;
if (args[0] == NULL)
{
return 1;
}
for (i = 0; i < num_commands(); i++)
{
if (strcmp(args[0], lookup_str[i]) == 0)
{
if (strcmp(args[0], "history") == 0 && strcmp(args[1], "-c"))
{
clear_history();
}
return (*lookup_func[i])(args);
}
}
return mysh_launch_process(args);
}
void mysh_loop(void)
{
char *line;
char **args;
int state;
do
{
printf("# ");
line = mysh_read_line();
mysh_add_history(line);
args = mysh_split_args(line);
state = mysh_execute(args);
free(line);
free(args);
} while (state);
}
int main(int argc, char **argv)
{
// run main program loop
mysh_loop();
file.close();
return EXIT_SUCCESS;
}
/* main shell processes END*/```