Guide to Relative Paths

I've been toying whith a project in Win7 making use of relative paths (and relative paths shortcuts) to start apps and open files and folders on removable drives. A rather common problem it seems, since USB sticks came around.
Then I realized how vague my ideas were about navigation in the directory structure, a must for forming relative paths. I started using computers in good 'ol DOS times, but all that primordial knowledge has just faded into a thick fog.
Thus I searched the web for some basic tutorial, a primer for absolute beginners. I might be real bad at searching but, rather surprisingly, I found nothing of the kind. Just scattered references (most about Unix or HTLM) and no organic Windows tutorial, not even for the use in the "Command Prompt" window.
The same happened when I searched for the creation of shortcuts using relative references.
Thence the idea to organize the collected fragments in personal memos for my future use and reference. Only later it occurred to me that some others might be interested in my findings. So I edited the lot and gave it the form of two small tutorials for navigational lubbers like me, the first of which, at the suggestion of the esteemed admin Brink, I'm posting hereunder.

Hopefully, quite a few knowledgeable eyes will scan this material for inaccuracy or/and incompleteness and offer corrections and additions, which are very warmly welcomed. Heck, I'm re-learning this stuff myself!

So, here we go.

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A BEGINNER'S GUIDE TO RELATIVE PATHS IN WINDOWS
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Relative paths have often the advantage of simplifing referencing data, particularly in combination with the Window system's environment variables.

When operating within removable external drives however, the possibility of defining relative paths to a file or a directory by their relative location to the current working directory (CWD) instead than relative to the root of a named drive, is a decisive asset.

All links and shortcuts located on esternal drives based on absolute paths and therefore relative to the root of a named drive, can become misleading and consequently useless when these drives are mounted on other computers and, with all probability, are assigned a different drive letter.

The downsides of relative paths are mainly two:

1. A relative path cannot span over different drives, thus making it impossible to reference data on other drives other than the local one.

2. When moving documents, applications and folders, all links and shortcuts referencing them must be accordingly moved as well, in order to maintain intact their relative route.

In order to succesfully use relative paths, it is necessary to have a clear idea of the conventions and switches making possible the navigation in the directory structure.
Below is a basic (for dummies) reminder of the elements of this navigation with regard to relative addressing.

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1. RELATIVE REFERENCE IN THE ROOT DIRECTORY
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Al directories and files on the system can be thought of as a tree growing upside-down from the root directory.
The "first" directory is called the root, and the parent directory of the root directory is the root itself. One can't go back in the file structure more than the that.

IN CMD.EXE
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In a "Command Prompt" window, the root directory is represented by the notation [drive_letter:], followed by a BACKWARD slash (\), for example:

C:\

To change to the root of another drive mounted in the system, just enter it's letter followed by a colon, for example:

E:

IN WINDOWS
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The root directory is represented by a FORWARD slash (/), the first one in the path string, as for example in the pathname:

C:/prices/fruit/apples.txt

As you can see, in path strings the FORWARD slash (/) is also used as a separator between directories.

If C: is the current drive, the above can also be expressed with the relative notation:

/prices/fruit/apples.txt

Which is interpreted as follows:

1. Start at the root (/) directory.
2. Move from / down to a directory named "Prices".
3. Move from "Prices" down to a directory named "Fruit".
4. The file "Apples.txt" is located in that directory.

Even if the pathname doesn't use a [drive_letter:] specification, the above example is actually a sort of absolute path in disguise, since the first slash (/) represents the root directory of the current drive, whichever that is. However, the fact that the drive is not referenced by name makes all the difference. It means that such a string, for example:

/travel/flight/info.txt

can also be used as a sort of "relative path", on external drives subject to changes of [drive_letter:] on other computers, where an absolute path making use of a specification like:

E:/travel/flight/info.txt

could become entirely useless.

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2. RELATIVE REFERENCE IN THE CURRENT WORKING DIRECTORY (CWD)
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IN CMD.EXE
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Files and folders located in the current working directory can be referenced directly by their name, for example when renaming or deleting them in a "Command Prompt" window:

del apples.txt

The commands "cd/" or "cd\", take you from whichever is the current working directory (CWD) to the root of the filesystem on the current drive.

IN WINDOWS
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A file in the current working directory is referenced using it's name, optionally preceded (mainly for readability in complex paths), by a dot and a slash (./). For example:

./apples.txt

refers to a file named "Apples.txt" in the current working directory (of the current drive since there is no [drive:] specification).

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3. RELATIVE REFERENCE TO A FILE OR FOLDER IN A SUBDIRECTORY OF THE CURRENT WORKING DIRECTORY
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IN CMD.EXE
----------------
From a "Command Prompt" window, you can move from the current working directory to one of it's subdirectories simply by using the command "cd" and the name of the subdirectory:

cd dirname

and can point to a file or folder in the subdirectory by it's name preceded by a BACKWARD slash (\), in it's turn preceded by the name of the subdirectory, as in:

fruit\apples.txt

IN WINDOWS
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A file or folder in a subdirectory of the current working directory is referenced by the name of the subdirectory followed by a FORWARD slash (/), followed in it's turn by the file or folder name.

fruit/apples.txt

Optionally (mainly for readability in complex paths), a dot and a FORWARD slash (./) may be placed before the string to represent, redundantly, the current working directory (of the current drive, since there is no [drive_letter:] specification):

./fruit/apples.txt

Both the paths above refer to a file named "Apples.txt" in the subdirectory "Fruit" located in the current working directory. Accordingly, the path:

fruit\apples\pics\sample.jpg

refers to a file called "Sample.jpg" located in directory "Pics", located in directory "Apples", located in directory "Fruit" which is, in it's turn, located in the current working directory (of the current drive, since there is no [drive_letter:] specification).

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4. RELATIVE REFERENCE TO A FILE OR FOLDER IN THE PARENT DIRECTORY
OF THE CURRENT DIRECTORY (CWD)
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IN CMD.EXE
----------------
From a "Command Prompt" window, you can move from the current working directory to it's parent (one level up) directory by using the command "cd" followed by a double dot and either a BACKWARD slash or a FORWARD slash:

cd ..\ (or cd ../)

In the same way, a file or folder in the parent directory of the current working directory, is referenced by it's name preceded by a double dot and a BACKWARD slash (..\). For example:

..\apples.txt

or even multiple levels above:

..\..\..\apples.txt

IN WINDOWS
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The pathnames use FORWARD slashes:

../fruit.txt

refers to a file named "Fruit.txt" in the parent directory of the current working directory (of the current drive since, unlike the first example, there is no [drive_letter:] specification).

And the pathname:

../../pears

refers to a directory named "Pears" in the directory two levels above the current working directory (of the current drive since there is no [drive_letter:] specification).

The following string:

D:../fruit.txt

while using the relative notation (../) is actually a absolute path, having a [drive_letter:] specification, and refers to a file called "Fruit.txt" located in the parent directory of the current working directory, which in it's turn is located in the root of drive C:

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5. RELATIVE REFERENCE TO A FILE OR FOLDER ON ANOTHER DRIVE
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IN CMD.EXE
----------------
From a "Command Prompt" window, this is achieved by using an absolute path combined with the change directory "cd" command.

While if you are, for example, on the C: drive, entering:

E:

will only take you to the root of the E: drive, while entering the command "cd" with the "/d" switch and a absolute path to a file or directory, as follows:

cd /d E:\pears

first switches to the E: drive, and then makes "Pears" the current working directory.

IN WINDOWS
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While the use of absolute paths according to the rules above is customary and unproblematic, the referral to files on other drives using relative notations is impossible, as a relative path cannot span over different drives.

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6. GENERAL PROCEDURE FOR FORMING RELATIVE PATHNAMES
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A relative pathname is given as a list of all directories on the route from the current working directory to the target file or directory, separated by FORWARD "/" slashes.

1. If the target is below the current directory, it is necessary to list all subdirectories on the route from the current directory to the target, separated by forward slashes "/.

2. If the target is above the current directory in the directory tree and in a straight path, that is to say always ascending, it is necessary to move up the file structure with one or more "../" consecutive notations until the parent directory containing the target is reached.

3. If the target is on another branch of the directory tree than the current directory, that is, it's path contains both ascending and descending steps, it is necessary to move up the file structure with one or more "../" consecutive notations until a directory located above the target is reached.
From there, as in point 1. above, all the directories in a straight descending path to the target must be listed, separated by forward slashes "/".

4. The name of the target file or folder must be appended to the resulting path.

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7. NOTE ABOUT SLASHES
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In Windows, both slash types, BACKWARD (\) and FORWARD (/) can generally be used interchangeably. Windows CMD Shell (cmd.exe) makes an exception.

The "Command Prompt" window likes BACKWARD slashes instead, as usually console programs use FORWARD slashes to define command switches.

A path containing forward slashes often needs to be surrounded by double quotes to disambiguate it from command line switches. For example:

E:\>dir "/Folder/SubFolder/"

To make things even more interesting, the "Command Prompt" command "cd" (change directory) does not follow this guideline all the way. As we have seen in sections 2. and 4. above:

"cd ..\" works as well as "cd ../", taking you to the parent directory of the current directory.

"cd\" works as well as "cd/", taking you from whichever is the current working directory (CWD) to the root of the filesystem on the current drive.

More:

"cd C:\apples" works as well as "cd C:/apples"

Also, from a ROOT folder, the command:

"cd C:.\Programs.\Internet"

would be treated the same as

"cd C:/Programs/Internet"

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That's it for now, folks.
The next little tutorial on the use of relative paths in shortcuts will be soon forthcoming.

Well, explained, good job!