Looping over multiple couples of endogeneous variables and intrument

[Marina Ngoma]

I am writing a do file where I run 3 regressions: (i) the OLS, (ii) the IV first stage, (iii) the IV 2SLS.
I have multiple variables to measure the endogenous explanatory variable; each of which have their own instrument.

Is there a way I can loop the 3 regressions over each couple of endogenous variable-IV?
I have 4 couples:
1. Endogenous variable is X1, their instrument is IV1
2. Endogenous variable is X2, their instrument is IV2
3. Endogenous variable is X3, their instrument is IV3
4. Endogenous variable is X4, their instrument is IV4

My regressions are:

       ** OLS
        reg `yvar' X1, robust
           
        ** IV First stage
        reg X1 IV1, robust
        
        ** 2SLS
        ivreg2 `yvar' (X1 = IV1), robust

How can I loop the three equations over each of the 4 couples X(n)-IV(n)?

Thanks,

[Andrew Musau]

Are the variables literally named X# and IV#?

forval i=1/4{
    ** OLS
        reg `yvar' X`i', robust
           
    ** IV First stage
        reg X`i' IV`i', robust
        
    ** 2SLS
        ivreg2 `yvar' (X`i' = IV`i'), robust
}

[Marina Ngoma]

Thank you, Andrew!