I was making an service for iptables, running iptables-restore and discovered that the StandardInput option does not allow me to set the standard input of an exec to a regular file.  This was a little surpirising since there are so many other process properties you can control as documented in the systemd.exec man page.

For iptables-restore, I worked around this limitation by creating the following wrapper script:

{code}
#!/bin/bash
in="$1"
shift
exec $* < "$in"
{code}

It would be nice to avoid the overhead of starting up a shell just to redirect the standard input.