How to print telnet response line by line?

Question

Is it possible to print the telnet response line by line, when a command executed over telnet keeps on responding over console ?

Example: I have executed a command (to collect logs), It keeps on displaying logs on console window. Can we read the response line by line & print it , without missing any single line ?

Below snippet writes the log, but only after certain specified time. If I stop the service/script (CTRL-C) in between, that doesn't write anything.

import sys
import telnetlib
import time


orig_stdout = sys.stdout
f = open('outpuy.txt', 'w')
sys.stdout = f

try:
        tn = telnetlib.Telnet(IP)
        tn.read_until(b"pattern1")
        tn.write(username.encode('ascii') + b"\n")
        tn.read_until(b"pattern2")
        tn.write(command1.encode('ascii') + b"\n")
        z = tn.read_until(b'abcd\b\n',600)
        array = z.splitlines( )
except:
        sys.exit("Telnet Failed to ", IP)

for i in array:
        i=i.strip()
        print(i)

sys.stdout = orig_stdout
f.close()

you are directing the output to f so how do you think you can print it to the screen? — Padraic Cunningham, Dec 31 '14 at 12:49
Working with telnet currently i made the observation that using `read_until` habors danger of leaving unread bytes in the telnet buffer. One tends to forget about those. E.g. in the above example we stop reading at "pattern1" and if there are still bytes after "pattern1" in the buffer we will first send the username and then read the bytes after "pattern1" up to "pattern2", so we rely on the fact that "pattern1" is really at the end of the buffer. It continues that every `read_until` may also read bytes left over from the`read_until`before.This way one may loose track off the telnet response. — Wör Du Schnaffzig, Aug 13 '21 at 12:46

score 6 · Accepted Answer · edited Apr 02 '20 at 03:42

6

You can use tn.read_until("\n") in a loop in order to read one line durint execution of your telnet command

while True:
    line = tn.read_until(b"\n")  # Read one line
    print(line)
    if b'abcd' in line:  # last line, no more read
        break

edited Apr 02 '20 at 03:42

VertigoRay

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answered Dec 31 '14 at 12:06

Mariusz Jamro

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Thank You Secator. That's exactly what i wanted. – Jackie James Jan 04 '15 at 15:08

score 2 · Answer 2 · answered Dec 31 '14 at 12:05

2

You can use the ready_very_eager, read_eager, read_lazy, and ready_very_lazy functions specified in the documentation to read your stream byte-by-byte. You can then handle the "until" logic on your own code and at the same time write the read lines to the console.

answered Dec 31 '14 at 12:05

dionyziz

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read_very_eager & read_eager both prints telnet response along with ' ' , which is not needed. Both prints ' ' , if no cooked data available. read_lazy & read_very_lazy both prints only ' ' . – Jackie James Jan 04 '15 at 15:18
I think this answer is underrated as `read_until` is suitable only, if you know what to expect. Also it has the danger of leaving unread data in the telnet queue which is read interferingly in the next round. – Wör Du Schnaffzig Aug 16 '21 at 13:22

How to print telnet response line by line?

2 Answers2