GFORTRAN_STDIN_UNIT—Unit number for standard inputThis environment variable can be used to select the unit number preconnected to standard input. This must be a positive integer. The default value is 5.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gfortran/GFORTRAN_005fSTDIN_005fUNIT.html