Performing HTTP requests with cURL using proxy

General way (config wide proxy):

export http_proxy=http://your.proxy.server:port/
export https_proxy=https://your.proxy.server:port/

or read man curl ;):

-x, --proxy <[protocol://][user:password@]proxyhost[:port]>

     Use the specified HTTP proxy. 
     If the port number is not specified, it is assumed at port 1080.
curl -x http://proxy_server:proxy_port --proxy-user username:password -L http://url