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## 3 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 for all units.
- GFORTRAN_UNBUFFERED_PRECONNECTED: Do not buffer I/O for preconnected units.
- GFORTRAN_SHOW_LOCUS: Show location for runtime errors
- GFORTRAN_OPTIONAL_PLUS: Print leading + where permitted
- GFORTRAN_DEFAULT_RECL: Default record length for new files
- GFORTRAN_LIST_SEPARATOR: Separator for list output
- GFORTRAN_CONVERT_UNIT: Set endianness for unformatted I/O
- GFORTRAN_ERROR_BACKTRACE: Show backtrace on run-time errors