#!/usr/bin/python
# -*- Coding: utf-8 -*-

import os
import sys
import time

class Command(object):
    keywords = ['exit', 'cd']
    def __init__(self, line):
        self.argv = line.split()
    def sync_run(self):
        if self.argv[0] in self.keywords:
            getattr(self, "do_%s" % self.argv[0])()
        else:
            pid = os.fork()
            if pid ==0:
                try:
                    os.execvp(self.argv[0], self.argv)
                except OSError:
                    print >>sys.stderr,\
                        "command not found: %s" \
                        % self.argv[0]      
                    sys.exit(0)
            else:
                print "Wait for child (%d)" % pid
                res = os.wait()
                print "(%d) child quit with %d" % res
    def do_cd(self):
        if len(self.argv) == 1:
            os.chdir(os.environ.get("HOME"))
        else:
            try:
                os.chdir(self.argv[1])
            except OSError:
                print >>sys.stderr,\
                    "cd: no such file or directory: %s" \
                    % self.argv[1]
    def do_exit(self):
        sys.exit(0)


while True:
    cmd = raw_input('$ ').strip()
    if cmd == "": continue
    Command(cmd).sync_run()