GFORTRAN_LIST_SEPARATOR—Separator for list output
This environment variable specifies the separator when writing list-directed output. It may contain any number of spaces and at most one comma. If you specify this on the command line, be sure to quote spaces, as in
$ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
a.out is the compiled Fortran program that you want to run.
Default is a single space.