The few characters
appended to a filename
that tell a user or application
what type of file it is.
The extension can be determined by examining
the filename and locating the last occurrence
of the period
. This is typically the fourth character from the end of the name, and the following characters describe what kind of file it is.
Files ending with .txt
, .Txt, .TXT and other variations are all files with Content-Type: text/plain
. These ascii
text files are readable by any text editor or viewer, such as Windows Notepad
. With *nix, most text files do not have extensions, though.
Some files do not have three character extensions, such as the Joint Photographic Experts Group .jpeg
format. These must be shortened to .jpg
when saved to a system that runs Windows 3.x
Some files have more than one dot, as well. A file called README.windows.txt does not have a ".windows.txt" extension, because only the characters after the last dot determine
the extension of a file. In this case, the extension is .txt.