msh.py

import os

def cat(f):
    return open(f).read()
    
def ls():
    return os.listdir('.')

def pwd():
    return os.getcwd()
    
def cd(d):
    os.chdir(d)

cmds = {
    'ls': ls,
    'pwd': pwd,
    'cd': cd,
    'cat': cat
}
    

def msh():
    while True:
        user_input = input('{}: '.format(pwd()))
        cmd, *params = user_input.split(' ')
        if cmd in ['exit', 'quit', 'q']:
            break
        result = cmds[cmd](*params)
        if result:
            print(result)