filename extension

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filename extension

(filename extension)
The portion of a filename, following the final point, which indicates the kind of data stored in the file.

Many operating systems use filename extensions, e.g. Unix, VMS, MS-DOS, Microsoft Windows. They are usually from one to three letters (some sad old OSes support no more than three). Examples include "c" for C source code, "ps" for PostScript, "txt" for arbitrary text.

NEXTSTEP and its descendants also use extensions on directories for a similar purpose.

Apart from informing the user what type of content the file holds, filename extensions are typically used to decide which program to launch when a file is "run", e.g. by double-clicking it in a GUI file browser. They are also used by Unix's make to determine how to build one kind of file from another.

Compare: MIME type.

Tony Warr's comprehensive list. Graphics formats.
References in periodicals archive ?
This ensures that data are secure unless the user specifically modifies the file extension (e.g., changing .xls to .old, then moving the file to another machine, and finally changing the extension back to .xls).
* File Types--displays the file types associated with a particular file extension and the application to be run if you double-click on the icon.
New filters will allow users to incorporate non-supported Vision document types, even obscure file extensions, into searches and resulting Vision streams.
All infected file attachments use the file extensions PI or.PIF (for example--PASSWORD.PIF), although the files are actually ordinary EXE files.
* The file extensions for particular file formats; and
Other programs allow users to also restrict by file extensions, sharing, for example, all .mp3 and .avi files, but none of the .doc or .pst files.
Naturally the largest chunk of this nearly pocket-sized tome is made up of the words that some of use every day (and a great many more that we don't) while a number of appendices at the back of the book offer lists of textual emoticons, acronyms, top-level domains and common file extensions.
The list of executable file extensions is already so long that it's not realistic to expect every employee to remember them all, and the list keeps growing.
One of the reasons a virus propogates so quickly is because attachment file extensions can be easily hidden from the uninitiated, so when you receive an attachment with a sinister payload, it could only be labelled <attachment.jpeg> as opposed to showing the full file type, IE.
While this made life simpler for people who didn't want to have to learn file extensions, it was confusing for Windows users.
The more singleminded has details about more than 1700 file extensions and directs you to the bulletin board of last resort /ext.htm where you can ask about totally baffling extensions.
The attachment appears to be a simple text file named LIFE--STAGES.TXT, but in reality the file ends with the extension .SHS, which is not visible even if the user's computer is configured to display all file extensions. When the attachment is activated, it introduces changes in the computer and mails out copies of itself to 100 randomly chosen addresses from the user's Microsoft Outlook address book.