Zero-byte file

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A zero byte file or zero length file is a computer file containing no data; that is, it has a length or size of zero bytes.

Zero byte files cannot be loaded or used by most applications. Even a file describing an empty word processor document, an image file with zero by zero dimensions, or an audio file of length zero seconds usually still contains metadata identifying the file format and describing some basic attributes of the file; it results in the file with some positive size. Some very simple formats do not use metadata, such as ASCII text files; these may validly be zero bytes (a common convention terminates text files with a one- or two-byte newline, however). Conversely, zero byte files must use some disk space to be indexed by a filesystem (though none for content, in most cases).

In some cases, zero byte files may be used to convey information like file metadata (for example, its filename may contain an instruction to a user viewing a directory listing such as documents-have-been-moved-to-partition-D, etc.); or to put in a directory to ensure that it is nonempty, since some tools such as backup and revision control software may ignore the empty directories.

There are many ways that could manually create a zero byte file, for example, saving empty content in a text editor, using utilities provided by operating systems, or programming to create it. On Unix-like systems, the shell command $ printf > filename results in a zero byte file filename. Zero byte files may arise in cases where a program creates a file but aborts or is interrupted prematurely while writing to it. Because writes are cached in memory and only flushed to disk at a later time (page cache), a program that does not flush its writes to disk or terminate normally may result in a zero byte file. When the zero byte file is made, file system does not record the file's content on storage, but only updates its index table.


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