Thank you all. I'll try the updated documentation.
It would be very nice if electrum generated a file to make the process easier. Something like:
electrum maketx <addr> <value> unsigned.tx
And then, on the offline node:
electrum signtx unsigned.tx signed.tx
And finally:
electrum sendtx signed.tx
I understand that using stream redirection can alleviate the problem on the final step, but the signing would still be very messy. It would be nice to have a simpler command line interface.