Python 2.7.5下通过Telnet连接CentOS本地服务获取输出失败的技术问询

Hey there, let's work through this telnet script issue step by step. I see you're using Python 2.7.5 (quick heads up: it's end-of-life now, but we'll focus on fixing your current script first) to interact with a local service on port 5555, and you're having trouble capturing the getcellstat output. Let's break down the problems and fix them one by one:

First, Fix the Obvious Typo #

In your original script, you have:

print(red)

But your captured output variable is named res—that's a simple typo! No wonder you didn't see any command output. Change that line to print(res) first.

Clean Up String/Byte Mixing & Command Execution #

Python 2 handles strings and bytes differently than Python 3, and telnetlib in Python 2 expects string inputs (not byte literals like b"\n"). Let's fix your write calls:

• When sending username and password, don't mix string variables with byte literals. Append a regular newline string instead:

  tn.write(user + "\n")
  tn.write(password + "\n")
  

  (Since password is already a string, no need to encode it in Python 2.)
• In your modified script, you forgot to add a newline to the getcellstat command—so the service never got the signal to execute it! Always end CLI commands with \n when using telnet:

  tn.write("getcellstat --cellid 1\n")
  

Adjust Read Timing & Prompt Matching #

Your read_until calls might be timing out before the prompt appears, or the match string isn't exactly what the service sends. Let's tweak these:

1. Increase timeout values: 5 seconds might not be enough for the service to respond, especially after running a command that generates output. Try setting timeouts to 10-15 seconds, or use None to wait indefinitely (use cautiously):

   tn.read_until("login: ", 10)
   

2. Verify exact prompt strings: Looking at your manual telnet output, after typing l2, the prompt briefly shows mnxt[/]# before switching to mnxt[/l2]#. Your script waits for the latter immediately, but a short delay or extra line might throw it off. Keep the existing match but give it more time.
3. Confirm the end marker: Your ****** RNTI List end****** marker is perfect for capturing full output—just make sure the timeout is long enough for the command to finish running:

   res = tn.read_until("****** RNTI List end******", 15)
   

Fix the Random "g" Output #

That odd "g" in your modified script's output is because you didn't send a newline with the getcellstat command. The service was still waiting for input, and read_very_eager() picked up a partial character from the buffer. Adding the \n to the command will resolve this.

Full Corrected Script Example #

Here's a revised version of your script with all these fixes:

#!/usr/bin/python
import telnetlib
import time

host = "127.0.0.1"
user = "root"
password = "mavenir"

tn = telnetlib.Telnet(host, 5555)
# Optional: Enable debug to see all sent/received data
# tn.set_debuglevel(1)

# Handle login flow
tn.read_until("login: ", 10)
tn.write(user + "\n")
tn.read_until("password: ", 10)
tn.write(password + "\n")

# Navigate to l2 context
tn.read_until("mnxt[/]#", 10)
tn.write("l2\n")
tn.read_until("mnxt[/l2]#", 10)

# Run command and capture output
tn.write("getcellstat --cellid 1\n")
# Short wait to ensure command finishes executing
time.sleep(2)
res = tn.read_until("****** RNTI List end******", 15)
print(res)

# Clean up the connection
tn.close()

Additional Tips #

• Migrate to Python 3: Python 2 is no longer supported, and Python 3's telnetlib handles bytes more explicitly, which avoids confusion like string/byte mixing.
• Use debug mode: Add tn.set_debuglevel(1) right after creating the Telnet object to see all incoming/outgoing data. This is invaluable for figuring out where the script gets stuck or mismatches prompts.
• Check for hidden characters: Ensure your match strings exactly match the service's output (e.g., no extra spaces, tabs, or case differences between mnxt and MNXT).

内容的提问来源于stack exchange，提问作者Huud Rych