Filename mangling
{{Short description|Translation of the file name for compatibility at the operating system level}}
{{about|the mangling of filenames for operating system compatibility|the concept of name mangling within compilers|name mangling}}
{{Refimprove|date=July 2007}}
The process of filename mangling, in computing, involves a translation of the file name for compatibility at the operating system level. It occurs when a filename on a filesystem appears in a form incompatible with the operating system accessing it. Such mangling occurs, for example, on computer networks when a Windows machine attempts to access a file on a Unix server and that file has a filename which includes characters not valid in Windows.
FAT Derivative Filesystem
{{main|File Allocation Table|8.3}}
=Legacy support under VFAT=
A common example of name mangling occurs on VFAT file systems on versions of Windows from Windows 95 onwards. The VFAT specification{{clarify|date=December 2016}} allows Long File Names (LFNs). For backwards-compatibility with MS-DOS and older Windows software, which recognizes filenames of a maximum of 11 characters in length with 8.3 format (i.e.: an eight-letter filename, a dot and a three-letter extension, such as autoexec.bat), files with LFNs get stored on disk in 8.3 format (longfilename.txt becoming longfi~1.txt), with the long file name stored elsewhere on the disk.
Normally{{clarify|date=December 2016}}, when using compatible Windows programs which use standard Windows methods{{which|date=December 2016}} of reading the disk, the I/O subsystem returns the long filename to the program — however, if an old DOS application or an old Windows application tries to address the file, it will use the older, 8.3-only APIs, or work at a lower level and perform its own disk access, which results in the return of an 8.3 filename. In this case, the filenames become mangled by taking the first six non-space characters in the filename and adding a tilde (~) and then a number to ensure the uniqueness of the 8.3 filename on the disk. This mangling scheme can turn (for example) Program Files into PROGRA~1. This technique persists today when people use DOSBox to play classic DOS games or use Windows 3.1 in conjunction to play Win16 games on 64-bit Windows.
Unix Filesystems
{{which|date=December 2016}}
Unix file names can contain colons or backslashes, whereas Windows interprets such characters in other{{which|date=December 2016}} ways. Accordingly{{clarify|date=December 2016}}, software could mangle the Unix file "Notes: 11\04\03" as "Notes_ 11-04-03" to enable Windows software to remotely access the file. Other Unix-like systems, such as Samba on Unix, use different{{clarify|date=December 2016}} mangling systems to map long filenames to DOS-compatible filenames (although Samba administrators can configure this behavior in the config file).{{cite book
|last= Eckstein
|first= Robert
|author2=David Collier-Brown |author3=Peter Kelly
|title= Using Samba
|url= http://oreilly.com/catalog/samba/chapter/book/ch05_04.html
|accessdate= 2009-10-23
|edition= 1st
|date= November 1999
|publisher= O'Reilly & Associates, Inc
|chapter= 5.4 Name Mangling and Case
}}
Mac OS
macOS's Finder displays instances of ":" in file and directory names with a "/". This is because the classic Mac OS used the ":" character internally as a path separator. Listing these files or directories using a terminal emulator displays a ":" rather than the "/" character, though.