2009-08-23 22:21:57

File extension issues

File extension association issues

File extensions are very often linked to more than one program in Windows and the users has to watchl if some application did not replace the default program association used for opening the file (in most cases by another program installation or first use of a program). Due to the big number of three letter file extensions there is a possibility that the default associated application does indeed open the correct file with desired file extension, but it is a completely different file type with other structure and internal file format that the assigned application cannot open correctly.

Completely opposite problem you probably want to resolve in most cases, is a situation, when Windows does not know file type you want to open. Windows is trying to open unknown file and to find associated program or action in the Windows registry and if none file association is present, you will see this message:

Windows is trying to open unknown file to operating system alert dialog box screenshot

Windows dialog box screenshot when you want to open unknown file

Click at thumbnail to enlarge the image and view it in its full size

You can try to discover what it is and what application is linked to file extension you don't know by using on-line search form on every page of File-Extensions.org website at the top left part under site logo.

Different file formats with the same file extension problems

Unfortunately, there is no central registry used for file extensions and its assigns to unique file type. There is only a couple of quality on-line resource sites (like File-Extensions.org) specializing at file extensions scope, deep collecting and creating this kind of information to help computer users. File-Extensions.org website maintains database of thousands file extension records, the number of file extensions in our library still growing and keeping database in a fresh state is a hard goal.

If you are a developer of your own file type, look at unknown and unassociated file extension list (the list is quite huge) or simple try to use our search box and check if chosen file exension is used or not.

We recommend you to do it this way - choose unassigned file extension for your file type and submit to us all needed additional information about your file type and application to avoid future file types conflict with same file extensions names.

File extension security related issues

A clear Microsoft's Windows installation has settings for displaying file names that file extensions are disabled by default for known file types in Windows Explorer. Known file extensions to operating system are completely hidden to users and appropriate actions for various file types are recognized by its file extension in the background and visually represented to users by graphic icons together with base file name without extension.

This is due to Microsoft's policy that this way is maybe better for less advanced computer users, but it is also potentially dangerous for this same kind of users due security reasons. Microsoft prefers simplicity against security, because some dangerous and harmful files can be hidden under wrong file type and users do not have fully under control what they open or run. When showing file extensions is disabled users can run dangerous scripts or applications and harm their computer.

For example malicious users have tried to spread computer viruses and computer worms by using file names formed like "Somebody sended you Postcard.jpg.vbs or only Free-screensaver.scr (with vbs or scr file extension hidden by Windows and this will appear to user only as Postcard-for-you.jpg or Free-screensaver). A dangerous script or executable file looks like a common photo in .jpg image file format, but in this case written in Visual Basic Script, without alerting the user to the fact that it is a harmful computer program.

This security issue problem is still frequently discussed and we think that hiding file extensions by default is wrong decision, but situation is still the same (Windows 7 or Windows Vista included).

Later Windows versions (starting with Windows XP Service Pack 2 and Windows Server 2003) included customizable lists of filename extensions that should be considered malicious in certain cases of use, such as when files are downloaded from the web or received as an e-mail attachment. To protect against computer viruses, e-mail programs may prevent sending or receiving certain types of file attachments. Check your e-mail security settings to determine how attachments are handled.

Modern antivirus software solutions also help to defend users against such attempted attacks where possible.


Command name issues

The use of a filename extension in a command name appears occasionally, usually as a side effect of the command having been implemented as a script (in Bourne shell, Python, etc.) and the interpreter name being suffixed to the command name, a practice common on systems like Windows and MacOS, which rely on globally-set associations between filename extension and interpreter, but sharply deprecated in Unix-derived systems like Linux and Apple's OS X, where the interpreter is normally specified as a header in the script.

On association-based systems, the filename extension is generally mapped to a single, system-wide selection of interpreter for that extension (such as .py meaning to use 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 language is changed, the command name extension is changed as well, and the OS provides a consistent API by allowing the same extension-less version of the command to be used in both cases. This method suffers somewhat from the essentially global nature of the association mapping, as well as from developers' incomplete avoidance of extensions when calling programs, and that developers can't force that avoidance. Windows is the only remaining widespread employer of this mechanism.

On systems with interpreter directives, command name extensions have no special significance, and are by standard practice not used, since the primary method to set interpreters for scripts is to start them with an single line specifying the interpreter to use (which could be viewed as a degenerate resource fork).

Developers coming from association-based based culture to the interpreter directive culture often make the very distinctive error of including command name extensions. Embedding the implementation detail of the language used introduces a problem where the command's implementation language cannot be changed (for example, from shell to C++) without either breaking any tool that refers to the old script name, or retaining the now inaccurate old extension, both of which are generally considered harmful.

Filename case sensitive problem

When you moving files between different operating systems can present problems with recognition lowercase and uppercase letters in filename. For example, Microsoft Windows operating systems are case insensitive (Filename.doc, filename.doc, FileName.doc are still the same file to Windows, you can have only one file at the same directory and Windows does not allow you to create three files with this names) Also, if you name the file with lowercase letters and referring or accessing it with uppercase letters Windows still recognizes it and find this one file. However, under UNIX all three combinations of file names would be different files as UNIX file names are case sensitive and referring to files with wrong case sensitive name leads to various issues and errors when accessing the file.

The simple solution is to use only small letters for all your filenames and you don't need think about this problem.

Issues with burning files to CD or DVD

A data disc can contain files of any type. You can save .txt, .mp3, .html, or .doc type files or anything you want, but only with some limitations.

There are several file systems you can choose for the disc or more than only one at the same disc. Each of them is used for different applications. To select the appropriate file system depends on type of disc and data you want to burn. For more information see help section from your burning sofware or visit these Wikipedia articles: ISO 9660, Joliet and UDF.

If you use special characters or symbols in your file names (other than Roman charaters - ASCII [A-Z, 0-9]), this may cause problems if you try to burn that file to a disc. CD naming conventions are often more strict than common Windows naming conventions. The length of file names can be cut off by burning application together with file extension information and you will lose information about file types. Today's burning programs do check for errors before burning compilation (you must correct file naming errors manually, burn software can repair it for you, or skip these files from burning to disc), but basically very long file names or deep directory structure can cause problems and your burned disc can contain corrupted, missing data or be unreadable by other computers or some players.


Additional resources and credits to Wikipedia, the free encyclopedia: Computer security, Filename extension, Computer file, File format

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