Zero-byte file

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 $ touch 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.