To use the curl command with a proxy server that requires a username and password, you can use the -x option to specify the proxy server and the -U option to specify the username and password.
For example, to send a request to https://www.example.com using a proxy server at proxy.example.com with the username user and the password password, you can use the following command:
curl -x proxy.example.com -U user:password https://www.example.com
This will send a request to https://www.example.com using the proxy server at proxy.example.com, and include the username and password in the request.
If you want to specify the proxy server and username/password in the http_proxy environment variable, you can use the --proxy-user option to specify the username and password.
For example:
export http_proxy=proxy.example.com curl --proxy-user user:password https://www.example.com
This will set the http_proxy environment variable to proxy.example.com, and include the username and password in the request.
Keep in mind that the -x and --proxy-user options are not compatible with the -L option, which is used to follow redirects. If you need to follow redirects, you can use the --location-trusted option instead.
For more information about how to use the curl command with a proxy server that requires a username and password, you can consult the curl documentation or seek assistance from a qualified Linux or Unix administrator.