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File without extension

A file without an extension has no type suffix in its name. The name alone does not show the format, thus software must examine the content to identify the type. Common examples are README files, license texts, and program files on Unix systems. Many of these files contain plain text, and a text editor can show them.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.