int main(void) {
pid_t pid;
int argc, status;
char command[MAXLINE], *argv[MAXARGS], path[MAXPATH];
printf("Welcome to the mini-shell, msh!\n");
for (;;) {
printf("msh > ");
fflush(stdout);
fgets(command, MAXLINE, stdin);
argc = parse_input(command, argv);
/* if nothing is entered do nothing */
if (*argv == NULL) continue;
/* exit */
if (strcmp("exit", argv[0]) == 0) exit(EXIT_SUCCESS);
/* print working directory */
if (strcmp("pwd", argv[0]) == 0) {
printf("%s\n", getenv("PWD"));
continue;
}
/* error handling for invalid commands */
if (*argv[0] == '<' || *argv[0] == '>') {
_exit_error("No command.", false);
continue;
}
/* cd */
if (strcmp("cd", argv[0]) == 0) {
// not Kansas
if (argc > 1) chdir(argv[1]);
// Kansas, there is no place like home Toto.
else chdir(getenv("HOME"));
// lets make sure to update PWD.
getcwd(path, MAXPATH);
setenv("PWD", path, 1);
continue;
}
pid = fork();
/* Unable to fork, reached fork limit? */
if (pid == -1) perror("Shell programming error, unable to fork.\n");
/* inside the child process */
else if (pid == 0) process_input(argc, argv);
/* inside the parent process, waiting on child */
else {
if (wait(&status) == -1) perror("Shell program error");
else printf("Child returned status: %d\n", status);
}
}
return 0;
}
/* Executes a simple command that is not a builtin function, redirecting input
* and output as appropriate. As with all exec_XXX() functions, assumes that
* the parent has forked if necessary. Does not return.
*
* @simple = CMD to be executed
*/
void exec_simple(CMD* simple)
{
if (simple->fromFile && redirect_input(simple) < 0) _exit(EXIT_FAILURE);
if (simple->toFile && redirect_output(simple) < 0) _exit(EXIT_FAILURE);
assert(simple && simple->type == SIMPLE);
execvp(simple->argv[0], &simple->argv[0]);
_exit_error(EXIT_FAILURE); // execvp only returns on an error
}
/* Executes a stage that is not a builtin command. Delegates to exec_simple()
* and exec_subcmd() as appropriate. As with all exec_XXX() functions, assumes
* that the parent has forked if necessary. Does not return.
*
* @stage = CMD to be executed
*/
void exec_stage(CMD* stage)
{
assert(!is_builtin(stage));
if (stage->type == SIMPLE) {
exec_simple(stage);
} else if (stage->type == SUBCMD) {
exec_subcmd(stage);
} else { // Should never hit here
assert(false);
_exit_error(EXIT_FAILURE);
}
}
void process_input(int argc, char **argv) {
int fd;
bool flag = false;
for (int i = 0; i < argc; i++) {
if (argv[i][0] == '<') {
// error checking
if (flag) _exit_error("Can't have two input redirects.", true);
if (argv[i + 1] == NULL) _exit_error("No input redictions file specified.", true);
// open a fd
if((fd = open(argv[i + 1], O_RDONLY)) < 0) perror("open");
// dup the fd and close the fd
if(dup2(fd, 0) < 0) perror("dup2");
close(fd);
argv[i] = NULL;
flag = true;
} else if (strcmp(">", argv[i]) == 0) {
if (argv[i + 1] == NULL) _exit_error("No output file specified.", true);
if ((fd = open(argv[i + 1], O_TRUNC | O_WRONLY | O_CREAT, 0666)) < 0) perror("open");
if (dup2(fd, 1) < 0) perror("dup2");
close(fd);
argv[i] = NULL;
} else if (strcmp(">>", argv[i]) == 0) {
if (argv[i + 1] == NULL) _exit_error("No output file specified.", true);
if ((fd = open(argv[i + 1], O_APPEND | O_WRONLY | O_CREAT, 0666)) < 0) perror("open");
if (dup2(fd, 1) < 0) perror("dup2");
close(fd);
argv[i] = NULL;
}
}
if (execvp(*argv, argv) == -1) {
perror("process_input, shell program.");
_exit(-1);
}
}
