[systemd-devel] transforming Iptables bash script to systemd service file -help

[lux-integ]

Greetings,

I am attempting to learn to use systemd.  I have  an IPtbales script I intend 
to transform from a bash script to a systemd service file.

It has lines such as 
iptables -A INPUt -p tcp  ......-j ACCEPT
which I intend to  transform to
ExecStart=iptables -A INPUT -p tcp  ......-j ACCEPT

however it has  'conditionally-processed lines like  these
if [ something=1 ];
iptables -A INPUT -p tcp  ......-j ACCEPT
fi

where $something is an environmental variable set in an external file.

I read hrough   the systemd manual page on unit files
( http://www.freedesktop.org/software/systemd/man/systemd.unit.html )
 and the closet match I see is the use of two lines
ConditionFileNotEmpty=SomeFile
ConditionNull=0
where I presume one could create  'SomefFile' with something in it to trigger 
a logical 0  so avoiding processing the service file.  
If I am not wong  this would only relate to  the processing of a service file 
that that  THIS unit file relates to.

And this would conflict with my requirement as I want  ONE largish IPtables 
service file.  

The question is;  is there a way of conditionally procesing lines in systemd 
service files such as the following

ExecStart=/path/to/executible1
ExecStart=/path/to/executible2
  some condition satisfied  ( for example ConditionFileNotEmpty=SomeFile ..... 
)
ExecStart=/path/to/executible3
..back to  'unconditional processing
ExecStart=/path/to/executible4


I also read through the service file manual-page
( http://www.freedesktop.org/software/systemd/man/systemd.service.html )


and  I am wondering if 
ExecStartPre=   and ExecStartPost=  
could be used and if so how so

Advice  will be appreciated
sincerely
luxInteg