This was originally posted on 2011-12-18 to http://andrewho.co.uk/weblog/patching-gnu-screen-on-mac-os-x-for-vertical-split
The ability in GNU screen to vertically split a display so that two windows are visible side-by-side (which is what GNU screen means by "vertical split") is not available in the latest stable release (4.0.3). It is, however, available in the latest HEAD slated for screen 4.1. Various distributions such as debian have merged the upstream changes into their stable versions; Mac OS X (10.7) is not one of them. Here's how to compile it in.
First, clone the latest HEAD (450e8f38 at the moment):
% git clone git://git.savannah.gnu.org/screen.git ./screen.git
% cd ./screen.git/src
% ./autogen.sh
Then apply all of Apple's patches to make it 10.7-friendly. Some of the patches will need to be manually applied as HEAD has diverged a bit from 4.0.3:
% for x in Makefile.in config.h.in configure process.c pty.c screen.c \
> window.c; do
% curl "http://www.opensource.apple.com/source/screen/screen-16/patches/${x}.diff?txt" \
> | patch -p0
% done
Finally, there's one header file that needs to be included:
% curl -O http://launchd.macosforge.org/trac/export/23964/trunk/launchd/src/vproc_priv.h
Then compile the source and you're done:
% ./configure --prefix=/usr/local
% make
% sudo make install
awesome!