What characters should be restricted from a Unix file name?

blm_54213 0
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Consider a Save As dialog with a free text entry where the user enters a file name as free text, then clicks a Save button. The software then validates the file name, and saves the file if the name is valid.

On a Unix file system, what rules should be applied in the validation such that:

  • The name will not be difficult to manipulate later in terms of escaping special characters, etc.
  • The rules are not so restrictive that saving a file becomes non-user-friendly.

So basically, what is the minimum set of characters that should be restricted from a Unix file name?

validation unix file
7 Answers

The minimum are slash ('/') and NULL ('\0')

mouviciel_452490

Firstly, what you're describing is black listing. Your better option is to white list your characters, as it is easier (from a user perspective) to have characters inserted rather than taken away.

In terms of what would be good in a unix environment:

  • a-z
  • A-Z
  • 0-9
  • underscore (_)
  • dash (-)
  • period (.)

Should cover your basics. Spaces can be okay, but make things difficult. Windows users love them, unix/linux don't. So depending on your target audience choose accordingly.

LFSR_Consulting_332260

Often forgotten: the colon (:) is not a good idea, since it's commonly used in stuff like $PATH, i.e. the list of directories where executables are found "automatically". This can cause confusion with DOS/Windows directory names, where of course the colon is used in drive names.

unwind_281690

Do not forget that you can add a dot (.) at the beginning to hide files and folders... Otherwise, I'd follow a *NIX name convention (from Wikipedia):

Most UNIX file systems

  • Case handling: case-sensitive case-preservation
  • Allowed character set: any.
  • Reserved characters: /, null.
  • Max length: 255.
  • Notes: A leading . indicates that ls and file managers will not by default show the file

Link to wikipedia article about file names

Tobias_W228rre_210970

Let the user enter whatever name he wants. Artificially restricting the range of characters will only annoy the users and serve no real purpose.

user_435820
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