Below examples can also be used with ifort instead of gfortran.
Suppose trial1.f and trial2.f contain some subroutines. We can compile them without producing an executable by using below commands:
gfortran -c trial1.f
gfortran -c trial2.f
Above two commands will produce trial1.o and trial2.o files.
We can now combine them into one file by using below steps:
ar -cr libtrial.a trial1.o trial2.o
Suppose somefile.f uses the subroutines in trial1.f and trial2.f.
We can now compile somefile.f with below command:
gfortran somefile.f libtrial.a