#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <linux/limits.h>
#include <ctype.h>
#include <unistd.h>

void run(char *filename, char *cmd);

int main() {
    char input[ARG_MAX], cmd[ARG_MAX];

    while (1) {
        printf("$ ");
        fgets(input, ARG_MAX-1, stdin);

        // "ls"
        // "ls -la"
        // "kill -9 pid"

        // Read the command from the input
        int i;
        for (i = 0; i < ARG_MAX; i++) {
            if (i == 0 && input[i] == '\n')
                cmd[i] = '\0';
            else if (isspace(input[i])) {
                break;
            }
            else
                cmd[i] = input[i];
        }

        if (!strcmp("ls", cmd)) {
            run("/bin/ls", "ls");
        }
        else if (!strcmp("pwd", cmd)) {
            run("/bin/pwd", "pwd");
        }
        else if (!strcmp("ps", cmd)) {
            run("/bin/ps", "ps");
        }
        else if (!strcmp("kill", cmd)) {
            run("/bin/kill", "kill");
        }
        else {
            run(cmd, cmd);
        }
    }
    return 0;
}

void run(char *filename, char *cmd) {
    pid_t child = fork();
    if (child == 0)
        execlp(filename, cmd, NULL);
    else
        wait(child);
    return;
}