Portable Filenames

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In order to be able to move our media files from one computer to another it is critical that the names of our files can be understood by the different file systems and encodings they meet.

To find a set of characters which can meet all these criteria this article is originally based on content from Wikipedia Online Encyclopedia, especially the articles Filenames, Comparison of file systems and ASCII character encoding and Naming a File from MSDN. Please add other references to improve this article.

Recommendations

If you follow the rules below your file will be handled without issues on all of the following: servers, USB drives, CD's, DVD's, Blue Ray discs, HD DVD's, hard drives formatted with FAT32, NTFS, EXT2/3, Windows from '95 onwards, POSIX compliant systems (Linux, Unix, OSX) and much more...

Use only the following characters

  • a-z Lowercase alphabetical characters
  • A-Z Uppercase alphabetical characters
  • 0-9 Numerals
  • - Hyphens (Dashes)
  • _ Underscores

And only use them safely

  • a-z,A-Z Capital and small letters. Always use mixed case. MYFILE.txt can become myfile.txt without warning. MyFile.txt can not be changed without warning. (Windows ignores capitalisation)
  • - Hyphens must not start a file name.citation requested

There are limits to the maximum

  • number of nested directories must not be more than eight (root plus seven) (limit of ISO 9660)
  • number of directories to 65,535 (limit of ISO 9660) on Windows)
  • length of a file path to 256 characters (limit of Windows Path Size)
  • length of a file name to 255 characters (limit of Windows Path Size)
  • size of files to 4 GiB (limit of ISO 9660)

Some file names may not be used

  • CON, PRN, AUX, CLOCK$, NUL, COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9 (ref) also ., and .. (ref)


In Windows the space and the period are not allowed as the final character of a filename. The period is allowed as the first character, but certain Windows applications, such as Windows Explorer, forbid creating or renaming such files (despite this convention being used in Unix-like systems to describe hidden files and directories). Among workarounds are using different explorer applications or saving a file from an application with the desired name.

Some file systems on a given operating system (especially file systems originally implemented on other operating systems), and particular applications on that operating system, may apply further restrictions and interpretations. See comparison of file systems for more details on restrictions imposed by particular file systems.

In Unix-like systems, MS-DOS, and Windows, the file names "." and ".." have special meanings (current and parent directory respectively).

In addition, in Windows and DOS, some words might also be reserved and can not be used as filenames.<ref name="win"/> For example, DOS Device file:

CON, PRN, AUX, CLOCK$, NUL
COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9
LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.(ref)

Operating systems that have these restrictions cause incompatibilities with some other filesystems. For example, Windows will fail to handle, or raise error reports for, these legal UNIX filenames: aux.c, q"uote"s.txt, or NUL.txt.

Needing clarification

The following are not recommended but I can't find any reference to why they could be a problem. They are all ASCII characters.

{- | # | number sign | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reservedref |- | & | Ampersand | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved(ref) |- | ' | Apostrophe | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved(ref). Some websites have trouble handling file names containing apostrophes (PHP Bug #33198) |- | ( and ) | Parentheses | Template:Maybe | Unclear. Reference. |- | + | Plus | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved(ref) |- | , | Comma | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved(ref) |- | ; | Semi colon | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved(ref) |- | = | Equals sign | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. reference. |- | @ | At sign | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- | [ and ] | square brackets or box brackets | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- | ^ | Caret | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- | _ | Underscore | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- | ` | { and } | Curly brackets | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- | ~ | Tilde | style="background:#90ff90; color:black;" class="table-yes" | Yes | Not reserved. Reference. |- |}

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