Runtime (The GNU Fortran Compiler)

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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 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