storing the output of the command-line loop

Dear MEEP developers and users,

I have a problem with the following command:

for x in `seq a dx b`; do program  myfile.ctl; done

Using this command I have been able to run my ctl file several times and I can 
see the progress in the terminal.  However, the end file just has the data 
belonging to the last iteration of the loop. 

That is, at each iteration the file is overwritten. 
Please let me know how I can avoid this.

Also, I would appreciate it if someone clarifies the function of x=$x in this 
command. 

Many thanks,
Roya