# Specifying File Patterns

The filePatternList value given by the -filetypes option is a list of file patterns. Each file pattern is a list of the form
typeName {extension ?extension ...?} ?{macType ?macType ...?}?

typeName is the name of the file type described by this file pattern and is the text string that appears in the File types listbox. extension is a file extension for this file pattern. macType is a four-character Macintosh file type. The list of macTypes is optional and may be omitted for applications that do not need to execute on the Macintosh platform.

Several file patterns may have the same typeName, in which case they refer to the same file type and share the same entry in the listbox. When the user selects an entry in the listbox, all the files that match at least one of the file patterns corresponding to that entry are listed. Usually, each file pattern corresponds to a distinct type of file. The use of more than one file pattern for one type of file is only necessary on the Macintosh platform.

On the Macintosh platform, a file matches a file pattern if its name matches at least one of the extension(s) AND it belongs to at least one of the macType(s) of the file pattern. For example, the C Source Files file pattern in the sample code matches with files that have a .c extension AND belong to the macType TEXT. To use the OR rule instead, you can use two file patterns, one with the extensions only and the other with the macType only. The GIF Files file type in the sample code matches files that either have a .gif extension OR belong to the macType GIFF.

On the Unix and Windows platforms, a file matches a file pattern if its name matches at least one of the extension*(s) of the file pattern. The *macTypes are ignored.

## Specifying Extensions

On the Unix and Macintosh platforms, extensions are matched using glob-style pattern matching. On the Windows platform, extensions are matched by the underlying operating system. The types of possible extensions are:
1. the special extension “*” matches any file;
2. the special extension “” matches any files that do not have an extension (i.e., the filename contains no full stop character);
3. any character string that does not contain any wild card characters (* and ?).

Due to the different pattern matching rules on the various platforms, to ensure portability, wild card characters are not allowed in the extensions, except as in the special extension “*”. Extensions without a full stop character (e.g. “~”) are allowed but may not work on all platforms. .