The environment variable named GFORTRAN_UNBUFFERED_PRECONNECTED controls whether I/O on a preconnected unit (i.e. STDOUT or STDERR) is unbuffered. If the first letter is `y', `Y' or `1', I/O is unbuffered. This will slow down small sequential reads and writes. If the first letter is `n', `N' or `0', I/O is buffered. This is the default.