use of 2 covariate files for association analysis in plink

Dear all,
I want to use 2 covariate file in my association analysis in plink, is this possible ?, (without combining all the covariates in 1 file)
Is it valid to use ?
–bfile file
–logistic
–covar /covarfile1.txt
–covar-number 1-3
–covar/covarfile2.txt
–covar-number2-3
–out filename
Thanks