Test a WebSocket using curl.

curl-websocket.sh

curl --include \
     --no-buffer \
     --header "Connection: Upgrade" \
     --header "Upgrade: websocket" \
     --header "Host: example.com:80" \
     --header "Origin: http://example.com:80" \
     --header "Sec-WebSocket-Key: SGVsbG8sIHdvcmxkIQ==" \
     --header "Sec-WebSocket-Version: 13" \
     http://example.com:80/

okay, changing Sec-WebSocket-key with the one provided from browser works (not sure why):

curl --include \
     --no-buffer \
     --header "Connection: Upgrade" \
     --header "Upgrade: websocket" \
     --header "Host: localhost:8080" \
     --header "Origin: http://localhost:8080" \
     --header "Sec-WebSocket-Key: 3tMWYzcHwmObiLR3nWOgsg==" \
     --header "Sec-WebSocket-Version: 13" \
     http://localhost:8080/
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: YLxhg+bEzrZXCaOyyI5QkRBIdT4=

�       something

EDIT:
after reading the wikipedia, turned out it just a random 16-byte encoded with base64, on Linux, you can generate it with:

head -c 16 /dev/urandom | base64

This was very helpful. Thanks so much. In my case I just needed to confirm that the websocket server could be connected to and the connection would be upgraded, but I see how the headers and other settings can be changed as needed for any particular situation.