## 18 Data Files ¶

The `units` program uses four default data files: the main data file, `definitions.units`; the atomic masses of the elements, `elements.units`; currency exchange rates, `currency.units`, and the US Consumer Price Index, `cpi.units`. The last three files are loaded by means of ‘`!include`’ directives in the main file (see Database Command Syntax). The program can also use an optional personal units data file `.units` (`unitdef.units` under Windows) located in the user’s home directory. The personal units data file is described in more detail in Units Data Files.

On Unix-like systems, the data files are typically located in `/usr/share/units` if `units` is provided with the operating system, or in `/usr/local/share/units` if `units` is compiled from the source distribution. Note that the currency file `currency.units` is a symbolic link to another location.

On systems running Microsoft Windows, the files may be in the same locations if Unix-like commands are available, a Unix-like file structure is present (e.g., `C:/usr/local`), and `units` is compiled from the source distribution. If Unix-like commands are not available, a more common location is `C:\Program Files (x86)\GNU\units` (for 64-bit Windows installations) or `C:\Program Files\GNU\units` (for 32-bit installations).

If `units` is obtained from the GNU Win32 Project (http://gnuwin32.sourceforge.net/), the files are commonly in `C:\Program Files\GnuWin32\share\units`.

If the default main units data file is not an absolute pathname, `units` will look for the file in the directory that contains the `units` program; if the file is not found there, `units` will look in a directory `../share/units` relative to the directory with the `units` program.

You can determine the location of the files by running ‘`units --version`’. Running ‘`units --info`’ will give you additional information about the files, how `units` will attempt to find them, and the status of the related environment variables.