-y: specify python code to exec after connect¶

Warning

- Please BE CAREFUL not to expose your system with this functionality.

- Please DO NOT use this functionality for evil purposes.

pync can execute Python code in a separate process and connect the process’ stdin/stdout/stderr to the network socket.

Any data that comes in from the network will go to the process’ stdin, and any data that comes out from the process’ stdout/stderr will be sent out to the network.

There are two options that can provide this functionality, the lowercase -y option and the uppercase -Y option.

This section focuses on the -y option to execute code given as a string. To execute code from a specified file path, see -Y: specify python file to exec after connect.

Executing Python Code With -y¶

The lowercase -y option takes a string of python code to execute. This option is best used when you have a simple one-liner to execute.

For example, you can create a simple echo server by reading data from stdin (the network) and writing that same data back to stdout (the network):

Unix

pync -vly "import sys; sys.stdout.write(sys.stdin.read())" localhost 8000

Windows

py -m pync -vly "import sys; sys.stdout.write(sys.stdin.read())" localhost 8000

Python

import pync
pync.run('-vly "import sys; sys.stdout.write(sys.stdin.read())" localhost 8000')

To test this server, connect to it and send it a message:

Unix

echo Hello | pync -vq -1 localhost 8000

Windows

echo Hello | py -m pync -vq -1 localhost 8000

Python

import io
import pync

hello = io.BytesIO(b'Hello\n')
pync.run('-vq -1 localhost 8000', stdin=hello)

After receiving the message, the echo server should send it back to the client which then would display on the client console.

Here, we pass a negative number to the -q option to ensure pync doesn’t quit immediately after EOF on stdin (after sending the “Hello” message). Otherwise, there’s a chance the client would quit before receiving the message back from the echo server.

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