[jmaupay]

Here is my small contribution (with help of Andy).
I use that tcl script (cf. attached file) to convert .ac files from a dos command window.

Here is the header of that script for usage information:
# Exporter to batch ac3d.exe in a dos shell and converter a file to a new format.
# All AC3D export plugins are available.
#
# Installation: copy that file in the "scripts" directory of AC3D.
# That file must have the .tcl extension
#
# Usage: In a command window (cmd.exe):
# C:\> set AC3D_FILE_IN=<your input file>.ac
# C:\> set AC3D_FILE_OUT=<your output file>.yourextention
# C:\> set AC3D_FILE_CONVERTER=<the output converter to use>
# C:\> ac3d.exe
#
# Example: Convert a FileIn.ac to a FileOut.obj
# C:\> set AC3D_FILE_IN= D:\InputDir\FileIn.ac
# C:\> set AC3D_FILE_OUT= D:\OutputDir\FileOut.obj
# C:\> set AC3D_FILE_CONVERTER=OBJ
# C:\> ac3d.exe
#
# Remarqs:
# - The commands could be placed in a .bat file
# - Tested on AC3D 5.
# - AC3D_FILE_CONVERTER must contain a valid plugin name.
# - if AC3D_FILE_CONVERTER is not set, the list of available converters is displayed
# - an exporter plugin must be registered using the new ac_register_file_exporter, old method don't work