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7.2.2 Directory Names and Directory File Names

Directory Name

A directory name is a string that must name a directory if it names any file at all.

• see file-name-directory
• see file-name-as-directory

Directory File Name

A directory is actually a kind of file, and it has a file name (called the directory file name , which is related to the directory name but is typically not identical, e.g., it will not have a trailing slash.

• See directory-file-name

The Difference

These two names for the same entity are related by a syntactic transformation:

• On GNU and other POSIX-like systems, to obtain a directory name, append a ‘/’ to a directory file name that does not already end in ‘/’.

  directory name = directory file name + /
  

The difference between a directory name and a directory file name is subtle but crucial:

• When an Emacs variable or function argument is described as being a directory name, a directory file name is not acceptable.
• When file-name-directory returns a string, that is always a directory name.