shell.py

#!/usr/bin/python

import errno
import os.path
import shlex
import subprocess
import sys
import urllib2

prompt = "pyshell $ "
count = 0

class CommandError(Exception):
    pass

def read_file(filename):
    with open(filename, 'r') as fd:
        return fd.read()
    execfile('new_shell.py')

def write_code(new_code):
    code_file = __file__
    with open(code_file, 'w') as code_fd:
        code_fd.write(new_code)


def update(args):
    if len(args) != 1:
        raise CommandError("Usage: update <url>")
    try:
        filename = args[0]
        if filename[0] == ".":
            new_code = read_file(filename)
        else:
            fd = urllib2.urlopen(args[0])
            new_code = fd.read()
        print "New code:"
        print new_code
        ret = raw_input('Enter "y" to write this update: ')
        if ret == 'y':
            write_code(new_code)
            print 'Saved update.'
            print 'You may want the "reexec" command to run the new code.'
        else:
            print 'Your response "%s" was not "y", so update not saved.' % (ret, )
    except urllib2.URLError, e:
        print "Error downloading update: %s" % (e.reason, )

def cat(args):
    if len(args) != 1:
        raise CommandError("Usage: cat <file>")
    filename = args[0]
    if '/' in filename:
        raise CommandError("cat: bare filenames only (no slashes allowed)")
    try:
        print read_file(filename)
    except IOError, e:
        print "Failed to open %s" % (filename, )

def reexec(args):
    print "Re-execing the shell to pick up any updates..."
    sys.stdout.flush()
    os.execl(__file__, __file__, str(count+1))



username = None

def login(args):
    if len(args) != 1:
        raise CommandError("Usage: login username")

    global username
    if username:
        raise CommandError("Already logged in.")
    username = args[0]

def logout(args):
    if len(args) != 0:
        raise CommandError("Usage: logout")

    global username
    if not username:
        raise CommandError("Not logged in.")
    username = None

def status(args):
    if len(args) != 0:
        raise CommandError("Usage: status")

    if username:
        print "Logged in as %s" % (username, )
    else:
        print "Not logged in."

def show_help(args):
    print "Available commands:"
    for cmd in commands:
        print "- " + cmd


commands = {
    'update': update,
    'cat': cat,
    'login': login,
    'logout': logout,
    'status': status,
    'reexec': reexec,
    'help': show_help,
}

def run_command(cmd, args):
    print "Running %s with args %s" % (cmd, args, )
    if cmd in commands:
        try:
            commands[cmd](args)
        except CommandError, e:
            print e.message
    else:
        print "%s: command not found" % (cmd, )

def shell():
    try:
        while True:
            cmd_str = raw_input(prompt)
            args = shlex.split(cmd_str)
            if not args: continue
            cmd = args[0]
            run_command(cmd, args[1:])
    except EOFError:
        print "\nGoodbye!"

if __name__ == '__main__':
    if len(sys.argv) > 1:
        count = int(sys.argv[1])
        print "Starting shell (count %d)" % (count, )
    else:
        count = 1
    shell()