challenge3-3

mysh.py

import sys
import os
import subprocess

current = os.path.dirname(os.path.abspath(__file__))


def builtin_method(opt, piped_ret):
    global current
    opt_arr = opt.split()
    first = opt.split()[0]
    if first == 'cd':
        if len(opt_arr) == 1:
            target_path = '~'
        else:
            target_path = opt_arr[1]
        if os.path.exists(target_path) is False:
            print('invalid path: {}'.format(target_path))
            return True, None
        if os.path.isfile(target_path):
            print('file path is specified: {}'.format(target_path))
            return True, None
        current = os.path.abspath(target_path)
        os.chdir(target_path)
        return True, None
    elif first == 'echo':
        txt = opt[5:]
        return True, txt
    elif first == 'pwd':
        return True, current
    elif first == 'exit':
        exit(-1)
    else:
        return False, None


while True:
    cmd = input('mysh> ')

    if cmd == '':
        continue

    pipe_arr = cmd.split('|')
    last = ""
    pipe_idx = 0
    for c in pipe_arr:
        prev_ret = last
        if type(last) is bytes:
            prev_ret = last.decode('utf8')
        builtin, ret = builtin_method(pipe_arr[pipe_idx], prev_ret)
        if builtin is True:
            last = ret
        else:
            proc = subprocess.Popen(pipe_arr[pipe_idx],
                                    shell=True,
                                    stdin=subprocess.PIPE,
                                    stdout=subprocess.PIPE,
                                    stderr=subprocess.PIPE)
            proc_std, proc_err = proc.communicate(last)
            last = proc_std
            pipe_idx += 1
    if type(last) is bytes:
        ret = last.decode('utf8').strip()
    if ret is not None:
        print(ret)