Sorry for that I did't make myself clear in the last post. I want to append the coeffcient using temporary file. Here is the code and there is something wrong. How to solve the promlem? Thanks so much for your help in advance!
Code:
clear
input float(z x y dv iv)
3.3846154    5 3.2  4.944445 2.25
3.3846154    5 3.2 4.2222223    2
3.3846154    5 3.2  4.944445    2
3.3846154    5 3.2 4.3333335    2
3.3846154    5 3.2 4.7222223    2
3.3846154    5 3.2         4    2
3.3846154    5 3.2         4  2.5
3.3846154    5 3.2         4    2
        4 3.75 4.2  4.111111  3.5
        4 3.75 4.2 4.1666665 2.75
end

tempfile temp
save `temp'


foreach v of varlist x y z  {

        use `temp',clear

        tempfile file`v'
        local files "`files' file`v'"

        reg dv `v'
        gen coeffIV = el(r(table),1,1) 

        keep coeffIV

       save `file`v''


    }

append using `files'