Title here
Summary here
Environment Variables in Co-array Fortran
Our program demonstrates how to work with environment variables in Co-array Fortran. Environment variables are a universal mechanism for conveying configuration information to programs. Let’s look at how to set, get, and list environment variables.
program environment_variables
use iso_fortran_env
implicit none
character(len=:), allocatable :: foo, bar
character(len=:), allocatable :: env_var
integer :: i, status
character(len=1024) :: buffer
integer :: count
! To set a key/value pair, use the setenv subroutine
! To get a value for a key, use the get_environment_variable subroutine
call setenv("FOO", "1", status)
call get_environment_variable("FOO", length=count, status=status)
allocate(character(len=count) :: foo)
call get_environment_variable("FOO", value=foo, status=status)
print *, "FOO:", foo
call get_environment_variable("BAR", length=count, status=status)
if (status == 0) then
allocate(character(len=count) :: bar)
call get_environment_variable("BAR", value=bar, status=status)
print *, "BAR:", bar
else
print *, "BAR: "
end if
! Use get_environment_variable to list all key/value pairs in the environment
print *
i = 1
do
call get_environment_variable(name=null(), value=buffer, length=count, status=status, trim_name=.true.)
if (status /= 0) exit
print *, buffer(1:count)
i = i + 1
end do
end program environment_variablesTo compile and run the program:
$ gfortran -o environment_variables environment_variables.f90
$ ./environment_variables
FOO: 1
BAR:
TERM_PROGRAM=...
PATH=...
SHELL=...
...
FOO=1The list of keys in the environment will depend on your particular machine.
If we set BAR in the environment first, the running program picks that value up:
$ export BAR=2
$ ./environment_variables
FOO: 1
BAR: 2
...Note that Co-array Fortran doesn’t have a direct equivalent to Go’s os.Environ() function. Instead, we’ve used a loop with get_environment_variable to retrieve all environment variables. Also, string handling in Fortran is different from Go, so we’ve had to use allocatable character variables and handle string lengths explicitly.