This is the original vi in the earliest release of it's last version 3.7, released at October 31, 1981 on 4.1cBSD.

The software is downloaded with

git clone https://github.com/n-t-roff/ex-3.7.git

and can be kept up-to-date with

git pull

Some configuration (e.g. installation paths) can be done in the makefile. Three memory allocation methods can be configured:

• Traditionally ex uses sbrk. This does only work if malloc is not used by any called library function. To make ex work with today's libraries Heirloom's mapmalloc had been added. Use of this is not possible if the ASAN compiler feature is enabled.
• An alternative to Heirloom's mapmalloc is libmapmalloc from solaris. Unfortunately ex crashes on some systems with this library. The cause of this crash is likely a bug in the ex source code. If it is not intended to use libmapmalloc, the directory can be removed from the source tree to reduce license issues (libmapmalloc is CDDL licensed).
• malloc and realloc can be used instead of sbrk and mapmalloc. This is the default in the Makefile.

For compiling it on BSD, Linux and Solaris auto-configuration is required:

$ ./configure

The software is build with

$ make

and installed with

$ su
# make install
# exit

All generated files are removed with

$ make distclean

• This early release of version 3.7 did not support window resizing. That means that after starting vi the terminal size should be kept constant.
• The original vi (even the final 3.7 release from 1993) never had a showmode option. This option had been added to the solaris version of vi by SunOS developers and to heirloom vi by Gunnar Ritter.
• PAGE-UP, PAGE-DOWN keys may work on most terminals by putting map ^[[5~ ^B and map ^[[6~ ^F into ~/.exrc. If this doesn't work on your terminal you may need other escape sequences which can be retrieved with infocmp -l from capabilities kpp and knp. An example ~/.exrc may looks like (the map! commands make it possible to use PAGE and ARROW keys while staying in input mode):

    set autoindent
    " Only needed if "number" option is off
    set nowrapscan
    map  ^[[5~ ^B
    map! ^[[5~ ^[^Ba
    map  ^[[6~ ^F
    map! ^[[6~ ^[^Fa
    map  ^[OD   h
    map! ^[OD ^[i
    map  ^[OB   j
    map! ^[OB ^[ja
    map  ^[OA   k
    map! ^[OA ^[ka
    map  ^[OC   l
    map! ^[OC ^[la