CodeCrafters Shell

shell.py

import os
import subprocess
import sys

commands = ["echo", "exit", "quit", "type"]

command_path_cache = {}

def run_exit(input_values):
    try:
        if input_values[1]:
            i = int(input_values[1])
            if i >= 0 and i <= 255:
                return i
            else:
                return None
    except:
        return None
    # > the value shall be the exit value of the last command
    #   executed, or zero if no command was executed.
    return 0


def run_echo(input_values):
    [sys.stdout.write(f"{i} ") for i in input_values[1:]]
    sys.stdout.write("\n")


def run_type(input_values):
    arg = input_values[1]

    if arg in commands:
        sys.stdout.write(f"{arg} is a shell builtin\n")
        return 0

    command_path = get_command_path(arg)

    if command_path:
        sys.stdout.write(f"{arg} is {command_path}/{arg}\n")
        return 0

    sys.stdout.write(f"{arg}: not found\n")
    return 1


def get_command_path(command):
    if command in command_path_cache:
        return command_path_cache[command]

    for path in os.environ["PATH"].split(sep=":"):
        if os.path.exists(path) and command in os.listdir(path):
            command_path_cache[command] = path
            return path

    command_path_cache[command] = None
    return None


def main():
    while True:
        sys.stdout.write("$ ")

        input_values = input().split()
        command = input_values[0]

        if command == ("exit" or "quit"):
            return run_exit(input_values)
        elif command == "echo":
            run_echo(input_values)
        elif command == "type":
            run_type(input_values)
        else:
            if get_command_path(command):
                sys.stdout.write(subprocess.run(input_values, capture_output=True).stdout.decode('utf-8'))
            else:
                sys.stdout.write(f"{command}: command not found\n")

if __name__ == "__main__":
    main()