Capturing serial output

[Tension]

copy dh0:file to AUX:
copy AUX: to dh0:file

Make sure serial settings match on both Amigas.

Or use ProNet, I swear by it.

http://ftp.uni-paderborn.de/aminet/aminet/comm/net/ProNET34.lha

Its very easy to set up, I used it for years with no problems.
You can use a 3-wire serial cable, 7-wire serial cable, or a parallel cable.

Good luck!