作为一个python小白，在查找expect的替代中发现了依云用python写得expect.py。阅读后，发现很多都不明白，遂决定一一百度分析一下，另外还需要更改功能，遂记录之。
依云：expect.py
import fcntl #文件锁
import os
import re
from select import select #异步socket
import signal
import sys
import termios #for tty io control
import tty
class Expect:
buffer = b''
encoding = sys.getdefaultencoding()
def __init__(self):
self.master, self.slave = os.openpty()
self._old_winch = signal.signal(signal.SIGWINCH, self._size_changed)
self._size_changed()
try:
os.set_inheritable(self.slave, True)
except AttributeError:
pass
def spawn(self, cmd, *, executable=None, preexec_fn=None):
if executable is None:
executable = cmd[0]
pid = os.fork()
if pid == 0:
slave = self.slave
os.dup2(slave, 0)
os.dup2(slave, 1)
os.dup2(slave, 2)
os.close(slave)
if preexec_fn is not None:
preexec_fn()
os.execvp(executable, cmd)
elif pid > 0:
os.close(self.slave)
return
else:
raise RuntimeError('os.fork() return negative value?')
def expect_line(self, regex):
if isinstance(regex, str):
regex = regex.encode(self.encoding)
if isinstance(regex, bytes):
regex = re.compile(regex)
if not isinstance(getattr(regex, 'pattern', b''), bytes):
raise TypeError('regex must be one of type str, bytes or regex of bytes')
fd = self.master
outfd = sys.stdout.fileno()
buf = self.buffer
try:
while True:
if buf:
data = buf
else:
data = os.read(fd, 4096)
os.write(outfd, data)
data = data.split(b'\n', 1)
if len(data) == 2:
data, buf = data
else:
data = data[0]
if regex.search(data):
return
finally:
self.buffer = buf
def _read_write(self, data):
fd = self.master
outfd = sys.stdout.fileno()
to_write = len(data)
while to_write:
try:
r, w, e = select([fd], [fd], [])
if r:
rdata = os.read(fd, 4096)
os.write(outfd, rdata)
if w:
written = os.write(fd, data)
data = data[written:]
to_write -= written
except InterruptedError:
continue
def send(self, data):
if isinstance(data, str):
data = data.encode(self.encoding)
self._read_write(data)
def interact(self):
pfd = sys.stdin.fileno()
cfd = self.master
outfd = sys.stdout.fileno()
old = termios.tcgetattr(pfd)
old_signal = signal.signal(signal.SIGCHLD, self._interact_leave)
tty.setraw(pfd)
try:
while True:
try:
r, w, e = select([pfd, cfd], [], [])
for fd in r:
data = os.read(fd, 4096)
other = outfd if fd == cfd else cfd
os.write(other, data)
except InterruptedError:
continue
except OSError as e:
if e.errno == 5: # Input/output error: no clients run
break
else:
raise
except ChildProcessError:
pass
finally:
termios.tcsetattr(pfd, termios.TCSAFLUSH, old)
signal.signal(signal.SIGCHLD, old_signal)
def _interact_leave(self, signum, sigframe):
while os.waitid(os.P_ALL, 0, os.WEXITED | os.WNOHANG) is not None:
pass
def _size_changed(self, signum=0, sigframe=None):
size = fcntl.ioctl(sys.stdin.fileno(), termios.TIOCGWINSZ, '1234')
fcntl.ioctl(self.master, termios.TIOCSWINSZ, size)
def __del__(self):
if self._old_winch:
signal.signal(signal.SIGWINCH, self._old_winch)
解剖
依云自己给的用法是
import sys, expect
def main(host):
p = expect.Expect()
p.spawn(['ssh',host])
p.expect_line('# ')
p.send('ls\n')
p.interact()
if __name__ == '__main__':
host = '10.17.17.17'
if len(sys.argv) == 2:
host += sys.argv[1]
main(host)
这里需要手动键入ssh host的密码，且不退出当前连接。功能与我的需要有差异，就从这里入手分析，然后修改。
- 分析下类的初始化中都做了什么
os.openpty 用于打开一个新的伪终端时，返回pty与tty的文件描述符。
tty是各种类型设备的终端设备的简称
pty是虚拟终端。远程telnet登陆的就是pty
signal.signal用于绑定信号处理函数，修改进程收到信号以后的行为
SIGWINCH是窗口信号改变的信号
_size_changed中调用fcntl.ioctl(sys.stdin.fileno,termios.TIOCGWINSZ,'1234')获取当前窗口的长宽。
os.set_inheritable用于为文件标识符设定可继承标识
fcntl
参考
2.spawn方法开启任务
spawn函数声明中位置参数与关键字参数混合的方法，起初查找时，只知道a,*a这种用法，不明白放在中间什么意思，后来查找后才明白，*号只是起到分隔的作用，*号本身并没有被用到。
python位置参数，关键字参数
os.fork创建子进程
python fork
os.dup2重定向pty输入输出至当前输入输出
os.execvp开启一个新进程，执行相应的cmd
python dup2
3.expect_line方法接收关键信息
isinstance判断变量类型，支持判断"int,float,str,bool,list,tuple,dict,bytes"。其中bytes类型是python3.x开始支持
python bytes