$ gem install gmail-tool
If you use rbenv, you should rehash:
$ rbenv rehash
Usage: gmail-tool [OPTIONS] COMMAND [ARGS]
Available commands:
compose Open a pre-filled compose message
help Displays help for a command
Options:
-h, --help Displays this help message
$ gmail-tool compose --to="email@example.com" --subject="subject" --body="some text"
This will call open on your system with a url to compose an email on Gmail.