Fortran Hello World Example: How To Write and Execute Fortran Program on Linux OS

Question: I would like to understand the basics of how to write and execute a Fortran program on Linux OS. Can you explain it with a simple example?

Answer: In this article, let us review very quickly how to write a basic Hello World Fortran program and execute *.f program on Linux or Unix OS.

1. Write a Hello World Fortran Program

Create helloworld.f program using the Vim editor as shown below.

$ vim helloworld.f

program hello
print *,"Hello World!"
end program hello

You can also write a shorter version of the hello world Fortran program as shown below.

$ vim helloworld.f

PRINT *,"Hello World!"
END

2. Make sure Fortran compiler is installed on your system

Make sure Fortran compiler is installed on your system as shown below.

$ whereis gfortran
gfortran: /usr/bin/gfortran /usr/share/man/man1/gfortran.1.gz

$ which gfortran
/usr/bin/gfortran

$ dpkg -l | grep gfortran
ii  gfortran                                   4:4.3.3-1ubuntu1                          The GNU Fortran 95 compiler
ii  gfortran-4.3                               4.3.3-5ubuntu4                            The GNU Fortran 95 compiler
ii  libgfortran3                               4.3.3-5ubuntu4                            Runtime library for GNU Fortran applications

Installing GNU Fortran compiler.

If you don’t have GNU Fortran compiler, install it as shown below.

$ sudo apt-get install gfortran

3. Compile the Fortran program

Compile the helloworld.f using gfortran command as shown below. This will create the a.out file.

$ gfortran -ffree-form helloworld.f

$ ls -l
-rw------- 1 ramesh ramesh   55 Oct 24 23:13 helloworld.f
-rwx------ 1 ramesh ramesh 9545 Oct 24 23:14 a.out*

4. Execute the Fortran program (a.out)

$ ./a.out 
 Hello World!

$ mv a.out helloworld

$ ./helloworld 
 Hello World!