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(libc.info)File Name Resolution

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File Name Resolution
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   A file name consists of file name components separated by slash
(`/') characters.  On the systems that the GNU C library supports,
multiple successive `/' characters are equivalent to a single `/'
character.

   The process of determining what file a file name refers to is called
"file name resolution".  This is performed by examining the components
that make up a file name in left-to-right order, and locating each
successive component in the directory named by the previous component.
Of course, each of the files that are referenced as directories must
actually exist, be directories instead of regular files, and have the
appropriate permissions to be accessible by the process; otherwise the
file name resolution fails.

   If a file name begins with a `/', the first component in the file
name is located in the "root directory" of the process (usually all
processes on the system have the same root directory).  Such a file name
is called an "absolute file name".

   Otherwise, the first component in the file name is located in the
current working directory (Note: Working Directory).  This kind of
file name is called a "relative file name".

   The file name components `.' ("dot") and `..' ("dot-dot") have
special meanings.  Every directory has entries for these file name
components.  The file name component `.' refers to the directory
itself, while the file name component `..' refers to its "parent
directory" (the directory that contains the link for the directory in
question).  As a special case, `..' in the root directory refers to the
root directory itself, since it has no parent; thus `/..' is the same
as `/'.

   Here are some examples of file names:

`/a'
     The file named `a', in the root directory.

`/a/b'
     The file named `b', in the directory named `a' in the root
     directory.

`a'
     The file named `a', in the current working directory.

`/a/./b'
     This is the same as `/a/b'.

`./a'
     The file named `a', in the current working directory.

`../a'
     The file named `a', in the parent directory of the current working
     directory.

   A file name that names a directory may optionally end in a `/'.  You
can specify a file name of `/' to refer to the root directory, but the
empty string is not a meaningful file name.  If you want to refer to
the current working directory, use a file name of `.' or `./'.

   Unlike some other operating systems, the GNU system doesn't have any
built-in support for file types (or extensions) or file versions as part
of its file name syntax.  Many programs and utilities use conventions
for file names--for example, files containing C source code usually
have names suffixed with `.c'--but there is nothing in the file system
itself that enforces this kind of convention.