Runtime: Influencing runtime behavior with environment variables

The behavior of the gfortran can be influenced by environment variables.

Malformed environment variables are silently ignored.

• TMPDIR—Directory for scratch files
• GFORTRAN_STDIN_UNIT—Unit number for standard input
• GFORTRAN_STDOUT_UNIT—Unit number for standard output
• GFORTRAN_STDERR_UNIT—Unit number for standard error
• GFORTRAN_UNBUFFERED_ALL—Do not buffer I/O on all units
• GFORTRAN_UNBUFFERED_PRECONNECTED—Do not buffer I/O on preconnected units
• GFORTRAN_SHOW_LOCUS—Show location for runtime errors
• GFORTRAN_OPTIONAL_PLUS—Print leading + where permitted
• GFORTRAN_LIST_SEPARATOR—Separator for list output
• GFORTRAN_CONVERT_UNIT—Set conversion for unformatted I/O
• GFORTRAN_ERROR_BACKTRACE—Show backtrace on run-time errors
• GFORTRAN_FORMATTED_BUFFER_SIZE—Set buffer size for formatted I/O
• GFORTRAN_UNFORMATTED_BUFFER_SIZE—Set buffer size for unformatted I/O