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Filename suffix that indicates the file'south type

A filename extension, file name extension or file extension is a suffix to the name of a computer file (eastward.thousand., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically delimited from the residual of the filename with a full terminate (catamenia), but in some systems^[ane] it is separated with spaces. Other extension formats include dashes and/or underscores on early on versions of GNU Linux and some versions of IBM AIX.^{[ citation needed ]}

Some file systems implement filename extensions as a feature of the file organization itself and may limit the length and format of the extension, while others treat filename extensions equally part of the filename without special distinction.

Usage [edit]

Filename extensions may be considered a type of metadata.^[ii] They are normally used to imply information about the manner data might exist stored in the file. The exact definition, giving the criteria for deciding what function of the file name is its extension, belongs to the rules of the specific filesystem used; usually the extension is the substring which follows the last occurrence, if any, of the dot character (example: txt is the extension of the filename readme.txt, and html the extension of mysite.alphabetize.html). On file systems of some mainframe systems such as CMS in VM, VMS, and of PC systems such as CP/M and derivative systems such equally MS-DOS, the extension is a split up namespace from the filename. Under Microsoft'south DOS and Windows, extensions such every bit EXE, COM or BAT indicate that a file is a program executable. In Os/360 and successors, the part of the dataset proper name post-obit the terminal menses is treated as an extension by some software, e.g., TSO EDIT, only it has no special significance to the operating system itself; the same applies to Unix files in MVS.

Filesystems for UNIX-similar operating systems exercise not divide the extension metadata from the residue of the file proper name. The dot character is simply another character in the main filename. A file proper noun may have no extensions. Sometimes it is said to have more than ane extension, although terminology varies in this regard, and most authors define extension in a fashion that doesn't allow more than than ane in the same file name. More than one extension normally represents nested transformations, such equally files.tar.gz (the .tar indicates that the file is a tar archive of one or more files, and the .gz indicates that the tar archive file is compressed with gzip). Programs transforming or creating files may add the appropriate extension to names inferred from input file names (unless explicitly given an output file name), but programs reading files commonly ignore the information; information technology is mostly intended for the human user. Information technology is more than common, peculiarly in binary files, for the file itself to contain internal metadata describing its contents. This model generally requires the full filename to be provided in commands, whereas the metadata arroyo oftentimes allows the extension to be omitted.

The VFAT, NTFS, and ReFS file systems for Windows likewise do not split up the extension metadata from the balance of the file name, and allow multiple extensions.

With the advent of graphical user interfaces, the effect of file management and interface behavior arose. Microsoft Windows immune multiple applications to be associated with a given extension, and different deportment were available for selecting the required awarding, such as a context menu offering a choice between viewing, editing or printing the file. The assumption was still that whatsoever extension represented a single file type; there was an unambiguous mapping between extension and icon.

The classic Mac Os disposed of filename-based extension metadata entirely; it used, instead, a distinct file type code to identify the file format. Additionally, a creator code was specified to determine which application would be launched when the file'southward icon was double-clicked. macOS, notwithstanding, uses filename suffixes, as well every bit type and creator codes, every bit a consequence of existence derived from the UNIX-similar NeXTSTEP operating system.

Improvements [edit]

The filename extension was originally used to determine the file's generic blazon.^{[ citation needed ]} The demand to condense a file's type into three characters frequently led to abbreviated extensions. Examples include using .GFX for graphics files, .TXT for plain text, and .MUS for music. However, because many different software programs have been made that all handle these data types (and others) in a variety of ways, filename extensions started to become closely associated with sure products—fifty-fifty specific product versions. For case, early WordStar files used .WS or .WSdue north , where northward was the program'due south version number. Also, conflicting uses of some filename extensions developed. One example is .rpm, used for both RPM Package Manager packages and RealPlayer Media files;.^[3] Others are .qif, shared by DESQview fonts, Quicken financial ledgers, and QuickTime pictures;^[4] .gba, shared by GrabIt scripts and Game Boy Accelerate ROM images;^[5] .sb, used for SmallBasic and Scratch; and .dts, beingness used for Dynamix Three Space and DTS.

Another operating systems that used filename extensions generally had fewer restrictions on filenames. Many immune full filename lengths of 14 or more characters, and maximum proper noun lengths up to 255 were not uncommon. The file systems in operating systems such every bit Multics and UNIX stored the file proper noun as a single string, not split into base name and extension components, allowing the "." to be just another character allowed in file names. Such systems mostly allow for variable-length filenames, permitting more than 1 dot, and hence multiple suffixes. Some components of Multics and UNIX, and applications running on them, used suffixes, in some cases, to indicate file types, but they did not apply them as much—for example, executables and ordinary text files had no suffixes in their names.

The High Performance File System (HPFS), used in Microsoft and IBM's Os/ii likewise supported long file names and did not dissever the file proper name into a name and an extension. The convention of using suffixes continued, even though HPFS supported extended attributes for files, allowing a file's type to be stored in the file every bit an extended attribute.

Microsoft'due south Windows NT's native file arrangement, NTFS, supported long file names and did not carve up the file name into a name and an extension, but again, the convention of using suffixes to simulate extensions continued, for compatibility with existing versions of Windows.

When the Cyberspace age first arrived, those using Windows systems that were still restricted to 8.3 filename formats had to create web pages with names ending in .HTM, while those using Macintosh or UNIX computers could utilise the recommended .html filename extension. This too became a problem for programmers experimenting with the Java programming linguistic communication, since it requires the four-letter of the alphabet suffix .coffee for source code files and the 5-letter of the alphabet suffix .course for Java compiler object lawmaking output files.^[six]

Somewhen, Windows 95 introduced support for long file names, and removed the 8.3 name/extension separate in file names from non-NT Windows, in an extended version of the usually used FAT file system chosen VFAT. VFAT first appeared in Windows NT three.5 and Windows 95. The internal implementation of long file names in VFAT is largely considered to be a kludge^{[ by whom? ]}, but information technology removed the of import length restriction and allowed files to have a mix of upper case and lower case letters, on machines that would not run Windows NT well.

Command proper noun issues [edit]

The utilize of a filename extension in a command proper name appears occasionally, normally equally a side effect of the command having been implemented as a script, east.g., for the Bourne beat out or for Python, and the interpreter name being suffixed to the control name, a practice common on systems that rely on associations between filename extension and interpreter, but sharply deprecated^[vii] in Unix-like systems, such as Linux, Oracle Solaris, BSD-based systems, and Apple tree's macOS, where the interpreter is normally specified as a header in the script ("shebang").

On association-based systems, the filename extension is more often than not mapped to a single, organization-wide selection of interpreter for that extension (such every bit ".py" meaning to utilize Python), and the command itself is runnable from the command line even if the extension is omitted (assuming appropriate setup is done). If the implementation linguistic communication is changed, the command name extension is changed as well, and the OS provides a consistent API by allowing the same extensionless version of the command to be used in both cases. This method suffers somewhat from the essentially global nature of the clan mapping, as well as from developers' incomplete abstention of extensions when calling programs, and that developers tin't force that avoidance. Windows is the only remaining widespread employer of this mechanism.

On systems with interpreter directives, including virtually all versions of Unix, command proper name extensions have no special significance, and are by standard practise not used, since the main method to set interpreters for scripts is to offset them with a single line specifying the interpreter to use (which could be viewed as a degenerate resource fork). In these environments, including the extension in a command name unnecessarily exposes an implementation detail which puts all references to the commands from other programs at future risk if the implementation changes. For example, it would exist perfectly normal for a vanquish script to exist reimplemented in Python or Cerise, and later in C or C++, all of which would change the proper noun of the control were extensions used. Without extensions, a program always has the same extension-less name, with just the interpreter directive and/or magic number changing, and references to the program from other programs remain valid.

Security bug [edit]

The default behavior of File Explorer, the file browser provided with Microsoft Windows, is for filename extensions to not be displayed. Malicious users have tried to spread computer viruses and computer worms past using file names formed like LOVE-LETTER-FOR-YOU.TXT.vbs. The hope is that this will appear as Beloved-LETTER-FOR-Yous.TXT, a harmless text file, without alerting the user to the fact that it is a harmful figurer program, in this case, written in VBScript. Default beliefs for ReactOS is to display filename extensions in ReactOS Explorer.

After Windows versions (starting with Windows XP Service Pack 2 and Windows Server 2003) included customizable lists of filename extensions that should be considered "dangerous" in certain "zones" of operation, such as when downloaded from the web or received equally an e-mail attachment. Modern antivirus software systems also help to defend users against such attempted attacks where possible.

Some viruses take advantage of the similarity between the ".com" top-level domain and the ".COM" filename extension by emailing malicious, executable command-file attachments under names superficially like to URLs (e.g., "myparty.yahoo.com"), with the upshot that unaware users click on email-embedded links that they think lead to websites but really download and execute the malicious attachments.

There have been instances of malware crafted to exploit vulnerabilities in some Windows applications which could cause a stack-based buffer overflow when opening a file with an overly long, unhandled filename extension.

The filename extension is just a marker and the content of the file does not accept to match it.^[8] This can be used to disguise malicious content. When trying to identify a file for security reasons, it is therefore considered unsafe to rely on the extension alone and a proper assay of the content of the file is preferred. For instance, on UNIX derived systems, it is not uncommon to find files with no extensions at all, every bit commands such as file (control) are meant to be used instead, and will read the file'south header to determine its content.

Alternatives [edit]

In many Internet protocols, such as HTTP and MIME email, the type of a bitstream is stated as the media type, or MIME type, of the stream, rather than a filename extension. This is given in a line of text preceding the stream, such equally Content-type: text/plain.

There is no standard mapping between filename extensions and media types, resulting in possible mismatches in interpretation between authors, web servers, and client software when transferring files over the Net. For example, a content writer may specify the extension svgz for a compressed Scalable Vector Graphics file, only a web server that does not recognize this extension may not send the proper content type application/svg+xml and its required compression header, leaving web browsers unable to correctly interpret and display the image.

BeOS, whose BFS file arrangement supports extended attributes, would tag a file with its media type every bit an extended attribute. The KDE and GNOME desktop environments associate a media blazon with a file past examining both the filename suffix and the contents of the file, in the manner of the file command, every bit a heuristic. They choose the application to launch when a file is opened based on that media blazon, reducing the dependency on filename extensions. macOS uses both filename extensions and media types, too as file type codes, to select a Compatible Type Identifier by which to identify the file type internally.

Meet also [edit]

• file (command)
• List of file formats
• List of filename extensions
• Metadata
• .properties

References [edit]

1. ^ "What Is a File?" (PDF). z/VM - Version 7 Release ane - CMS Primer (PDF). IBM. 2018-09-eleven. p. vii. SC24-6265-00. Ane matter you need to know virtually creating files with z/VM is that each file needs its ain three-role identifier. The outset function of the identifier is the file name. The second role is the file blazon. And the tertiary part is the file mode. These 3 file identifiers are oft abbreviated fn ft fm.
2. ^ Stauffer, Todd; McElhearn, Kirk (2006). Mastering Mac OS Ten. John Wiley & Sons. pp. 95–96. ISBN9780782151282 . Retrieved 2 October 2017.
3. ^ File Extension .RPM Details from filext.com
4. ^ File Extension .QIF Details from filext.com
5. ^ File Extension .GBA Details from filext.com
6. ^ "javac – Java programming linguistic communication compiler". Sun Microsystems, Inc. 2004. Retrieved 2009-05-31 . Source code file names must accept .java suffixes, grade file names must have .class suffixes, and both source and form files must have root names that identify the class.
7. ^ Commandname Extensions Considered Harmful
8. ^ "What Is a File Extension?".

External links [edit]

• Media related to Filename extensions at Wikimedia Commons
• Data Formats Filename extension at Curlie

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Source: https://en.wikipedia.org/wiki/Filename_extension

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