I got a function that checks whether the passed in file name is . or ... But I don't know how to name it properly. Something like IsCurrentOrParentDirectory() is ambiguous, since the function takes a file name and not a full path. (Intuitively a fellow programmer would expect passing /usr/ while I'm in /usr/ would return true, while this is actually not the case.)
Is there a technical term for these directory entries? If there is one, what is it?
From the POSIX standard:
The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.
So, really, if you want to check whether the filename is . or .. you would have to call it IsDotOrDotDot(), or, using the POSIX terminology of pathname resolution, IsPredecessorOrParentOfPredecessor(), or maybe even PointsToPredecessorOrParentOfPrecedessor() … you get the idea. The problem is that the latter terminology only makes sense when looking at full pathnames. But nobody would understand that anyway.
Considering that . and .. are valid filenames (just interpreted differently), you should just stick to what you have, relying on the meaning rather than how they are called internally.
.bash_history dot or not dot? I'm not sure if that function name is more descriptive than the open the OP proposed.
Commented
Jul 23, 2014 at 7:01
. or .., and not whether it just started with a .. Of course the OP's function name is more descriptive; I was just pointing him to how it's technically referred to.
IsDotOrDotDot() says pretty much nothing about what the function is doing at all.
Commented
Jul 23, 2014 at 7:22
IsDotOrDotDot. Anyone knowledgeable with filesystem concepts would instantly understand it. It is debatable whether .bash_history is “dot” because no context is provided then for the meaning of “dot”, but it is definitely NOT “dot or dot dot”.
Commented
Jul 23, 2014 at 14:46
. and .. are usually used to describe relative paths vs. absolute ones like /usr. I'd use this difference and declare the function as IsRelativeCurrentOrParentDirectory().
Be aware the dot-references may occur anywhere in the path. What about /usr/local/..?
The POSIX Standard, which slhck♦ usefully quoted, says,
The special filename dot shall refer to …. The special filename dot-dot shall refer to ….
(emphasis added).
So, while it’s not exactly technical,
it looks like “special filename” just might be the official name.
Your users would probably understand it if you called your function any of the following:
IsSpecialDirectory(), IsSpecialFilename(), or simply IsSpecialName().
Or you could go with IsStandardDirectory(), IsStandardFilename(), or IsStandardName().
This follows the Unix naming convention (standard input, standard output) for things
that are established for you automatically (in this case, by mkfs and mkdir).
IsAutomatic…() or IsDefault…(), on the other hand, probably are not intuitive enough.
IsMagicDirectory() so that's pretty close to that, but I think your wording is much more intuitive and appropriate (especially since it uses established naming conventions). Using IsSpecialFileName would even make it clear that the function does not receive a path but a single file (or directory, link, etc) name.
Commented
Jul 24, 2014 at 6:58
IsSpecialFile() would have been a bad suggestion. But I didn’t suggest that; I suggested IsSpecialFilename(). While the names sda1, console, kmem, myfifo and urandom are suggestive, they are not reserved and are not inherently special. But . and .. are inherently special filenames.
Commented
Jul 24, 2014 at 16:39
The only term I know of from the *nix world is CWD for Current Working Directory. That is actually quite often used. See, for example /proc/$$/cwd which is a link to the directory you run the command from.
I don't know of any standard name for .. apart from dot-dot and as @slhck pointed out that's not a good choice.
Posix is pretty ambiguous on speaking about parent-child directory relationships. As others have said, ./.. isn't helpful while talking or communicating with other humans.
File structures can be thought about as a tree data structure. Here, generally "parent" and "child" or "daughter" are sufficient to convey meaning. You'll see data structure textbooks carry this convention
Alternatively, it seems like trees can be talked about as "up" and "down" the tree. By convention, "up" means closer to the root directory, and "down" refers to the child(ren).
I think either IsCurrentOrUp() or IsCurrentOrParent() can be argued to be good practice for naming functions.
.and..are file names according to the POSIX standard. See my quote below. I'd say it's fine here as it's about general computing concepts.foo.bar,foo, ...) but not a path (foo/bar,/foo/, ...). But since directories, links, etc are files too, I will leave it like that.