FvwmPrompt
FvwmPrompt is the replacement of both FvwmConsole and FvwmCommand introduced in fvwm3. FvwmPrompt allows users to send commands directly to fvwm from a terminal, such as xterm. If FvwmPrompt is run with no arguments, then it will open up an interactive shell that can be used send fvwm commands one at a time. If FvwmPrompt is given a command, it will send that command to fvwm without opening the interactive shell.
FvwmPrompts communicates to fvwm via the FvwmMFL socket, and as such FvwmMFL must be running to use FvwmPrompt, so be sure to start FvwmMFL from your StartFunction:
AddToFunc StartFunction I Module FvwmMFL
The fvwm source will only build FvwmPrompt or FvwmConsole, not both, so you will only have access to one of the tools. Since FvwmPrompt is built using the Go language, it may not be built on all systems. If FvwmPrompt is not built, use FvwmConsole for an interactive console and FvwmCommand for a command line tool to send fvwm commands.