To set a proxy for Ubuntu using the command line, you can use the following steps:
1. Open a terminal window.
2. Run the command to open .bashrc file.
3. In the file that opens, add the following lines at the end of the file, writing or replacing PROXY_URL and PROXY_PORT with the appropriate values for your proxy server:
4. Press "CTRL + O" to save the changes and "CTRL + X" to exit the editor.
5. Run the command to apply the changes.
6. This sets the proxy for the current user only. If you want to set the proxy for the entire system, you can add the same lines to the /etc/environment file instead of ~/.bashrc
Note that this is a general method for setting a proxy for Ubuntu, and the exact steps may vary depending on the version of Ubuntu or the proxy server software you are using.