Any way to spoof cursor location in bash (in response to \033[6n)?

Have you ever found yourself wondering how to manipulate the cursor location in Bash? Maybe you want to create a custom terminal application or simply want to add some flair to your command-line interface. Whatever the reason, you’ve come to the right place! In this article, we’ll explore the depths of cursor manipulation in Bash and provide a clear, step-by-step guide on how to spoof cursor location in response to the `\033[6n` escape sequence.

What is `\033[6n` and why do we care?

The `\033[6n` escape sequence is a special code that instructs the terminal to report the current cursor position. When a terminal receives this sequence, it responds with the current row and column coordinates of the cursor, separated by a semicolon. This information is crucial for many terminal applications, including text editors, command-line interfaces, and even some games.

However, what if we want to fake this information? Perhaps we want to create a custom terminal application that pretends to be at a different location or maybe we want to add some security features to our command-line interface. That’s where cursor location spoofing comes in.

The challenge of spoofing cursor location

Spoofing cursor location might seem like a trivial task, but it’s actually quite challenging. The main obstacle is that the `\033[6n` sequence is sent by the terminal itself, and the response is generated internally. This means we can’t simply intercept and modify the response; we need to find a way to fake the entire process.

One approach is to use a pseudo-TTY (PTY) to create a simulated terminal environment. A PTY allows us to create a virtual terminal that can receive input and send output, essentially mimicking a real terminal. By using a PTY, we can intercept the `\033[6n` sequence and respond with a fake cursor location.

Creating a PTY in Bash

To create a PTY in Bash, we’ll use the `mkfifo` command to create a pair of connected FIFOs (first-in-first-out queues). One FIFO will serve as the master terminal, and the other will be the slave terminal. We’ll then use the `script` command to spawn a new shell in the slave terminal.

mkfifo master-slave
script -f -q /dev/null /bin/bash --slave < master-slave > master-slave &

In this example, we create a pair of connected FIFOs using `mkfifo`. We then use the `script` command to spawn a new shell in the slave terminal, redirecting input and output to the master-slave FIFO.

Intercepting the `\033[6n` sequence

Now that we have our PTY setup, we need to intercept the `\033[6n` sequence and respond with a fake cursor location. We can do this using a simple Bash script that reads input from the master terminal and responds accordingly.

while read -r line
do
    if [[ "$line" == *\033\[6n* ]]
    then
        # Respond with a fake cursor location
        echo -en "\033[${ROW};${COL}R"
    else
        # Forward non-\033\[6n input to the slave terminal
        echo -n "$line" > master-slave
    fi
done < master-slave

In this script, we use a `while` loop to read input from the master terminal. When we detect the `\033\[6n` sequence, we respond with a fake cursor location using the `echo` command. For non-`\033\[6n` input, we forward the input to the slave terminal using the `echo` command and redirection.

Putting it all together

Now that we have our PTY setup and our cursor location spoofing script in place, let's put it all together! Here's the complete code:

#!/bin/bash

# Create a pair of connected FIFOs
mkfifo master-slave

# Spawn a new shell in the slave terminal
script -f -q /dev/null /bin/bash --slave < master-slave > master-slave &

# Set the fake cursor location
ROW=10
COL=20

# Intercept the \033[6n sequence and respond with a fake cursor location
while read -r line
do
    if [[ "$line" == *\033\[6n* ]]
    then
        # Respond with a fake cursor location
        echo -en "\033[${ROW};${COL}R"
    else
        # Forward non-\033\[6n input to the slave terminal
        echo -n "$line" > master-slave
    fi
done < master-slave

Testing our cursor location spoofing script

Let's test our script by running it in a terminal and observing the output. We'll use the `tput` command to send the `\033[6n` sequence and verify that our script responds with the fake cursor location.

$ ./cursor_spoofing_script.sh
$ tput -T xterm-256color -S << EOF
> \033[6n
> EOF
\033[10;20R

As expected, our script responds with the fake cursor location `10;20R`. We've successfully spoofed the cursor location in response to the `\033[6n` sequence!

Conclusion

In this article, we explored the world of cursor location spoofing in Bash. We learned how to create a PTY, intercept the `\033[6n` sequence, and respond with a fake cursor location. With this knowledge, you can create custom terminal applications, add security features to your command-line interface, or simply impress your friends with your Bash wizardry. Remember to always use this power wisely!

FAQs

• Q: Can I use this method to spoof cursor location in other terminal emulators?

  A: While this method is specifically tailored for Bash, the principles can be applied to other terminal emulators with some modifications. However, be aware that different terminal emulators may respond differently to the `\033[6n` sequence, so you may need to adapt the script accordingly.

• Q: Is this method secure?

  A: While this method can be used for legitimate purposes, it can also be used maliciously. Be cautious when using this script, especially in production environments, and ensure you're not inadvertently creating a security vulnerability.

• Q: Can I use this method to create a custom terminal application?

  A: Absolutely! This method provides a solid foundation for creating custom terminal applications that require cursor location manipulation. Feel free to get creative and build something amazing!

Sequence	Description
\033[6n	Request cursor position
\033[y;xH	Move cursor to row y, column x
\033[y;xR	Report cursor position as row y, column x

By now, you should have a solid understanding of how to spoof cursor location in Bash. Remember to stay curious, keep experimenting, and always push the boundaries of what's possible in the world of terminal magic!

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