Absolute and Relative Paths

Transcription

1 Absolute and Relative Paths A path is the sequence of directories that must be traversed to get from one directory to another. (In the Windows world directories are often called "folders"; we will use the two terms as synonyms.) In order to work effectively at the command prompt, it is useful to know the basics of how to specify paths between directories and files. Directory Hierarchies Consider the directory structure shown in the figure below. This typical directory structure has a primary directory (usually called the root directory and designated on a PC by the symbol "\") that contains within it all other directories as subdirectories, and each directory so contained may itself contain subdirectories. In this example the root directory contains the directory Dir1, and this directory in turn contains the directories Dir2 and Dir5. Finally, Dir2 contains subdirectories Dir3 and Dir4, while Dir5 contains a subdirectory Dir6. The files on the system are contained in these directories. In the figure some representative files are illustrated in red. For example, the file index.html (see the green arrow) is contained in the directory Dir2, which is a subdirectory of Dir1, which is finally a subdirectory of the root directory. Directory Trees Another useful way to look at this directory structure is in terms of a Directory Tree. The above figure shows a tree diagram corresponding to the directory structure illustrated in the first figure. If we view this as a tree (fallen on its side), the branches of the tree correspond to the subdirectory structure. If you stand the directory tree upright, this analogy also makes clear why the master directory containing all other directories is termed the "root" directory.

2 Paths The directory tree diagram illustrates graphically the meaning of a path: it literally is a path: the (shortest) one that we would follow on the directory tree to go from one directory to another. For example, consider the files illustrated in the first diagram. Suppose we ask what the "path" is from the file index.html to the file file3.ext. The file index.html is in the directory Dir2 and file3.ext is in the directory Dir3. From the tree diagram, to get from index.html to file3.ext we must first go to the directory Dir3, which is contained in Dir2. We say that (relative to the file index.html) the file file3.ext is at the location Dir3\file3.ext. Likewise, relative to the directory Dir1, the file file3.ext is at Dir2\Dir3\file3.ext, and so on. Examples such as these are termed "specifying the relative path to a file" from some starting point. Specification of Paths Thus, the path to a file that lies in a subdirectory of your present directory is specified by listing, in order, the directories (omit the one that you are in) that you must pass through to get to the file, with backslashes after each directory name, and followed finally by the file name. Pretty simple, once you get the hang of it! But what if the file is not in a subdirectory of your present directory? For example, where is the file file6.ext (which is in Dir6) relative to the file index.html? The same rule applies as before, but the adjacent figure illustrates that to get to the directory Dir6 from the directory Dir2 we must first go BACK in the directory hierarchy until we reach a directory that contains Dir6 (and, of course, Dir2) in its subdirectory structure. Thus, to reach file6.ext from index.html we go back to Dir1, then to its subdirectory Dir5, and then to its subdirectory Dir6. The notation that is used to go back one level in a directory hierarchy is "..\" (two dots, followed by a backslash), and we may say that the location of file6.ext relative to index.html is..\dir5\dir6\file6.html, as illustrated in the preceding figure. Absolute (Full) and Relative Paths The examples of paths we have just been considering are termed "Relative Paths", because the location is specified relative to our present location. However, notice that we could also specify an "Absolute Path" or Full Path for files by going back to the root directory and writing the complete path to the file from there. In the previous example, the absolute path of file6.ext is C:\Dir1\Dir5\Dir6\file6.ext.

3 Notice the difference between absolute and relative paths: if I move the file index.html to a new directory, the address of file6.ext relative to index.html changes, but its absolute address remains the same. A Full or Absolute path always begins with a drive letter, is followed by a colon and an initial "\" (which stands for the root directory), followed by a list of the directories you must pass through to get to the file, with backslashes after each directory name and followed by the file name. A Relative Path will NEVER begin with a backslash. The existence of an initial backslash in a path tells the operating system to begin searching for the file or folder at the root. The absence of an initial backslash, tells the operating system to begin searching for the file or folder from your current position. The relative path to a file or folder that exists beneath your current directory is specified by listing, in order, the directories (omit the one that you are in) that you must pass through to get to the file, with backslashes after each directory name, and followed finally by the file name. Using leading periods to traverse backwards up the directory structure you can specify the relative path to a file or folder that does not exist beneath your current directory. Two leading periods move you back one subdirectory; three leading periods move you back two subdirectories; four leading periods move you back three subdirectories, and so on. An example of using leading periods in a path is included above. There are also some examples of its use in the below examples section of this document. *Note: Most books use the term Absolute Address or Absolute Path. I frequently refer to this as the Full Path; therefore, the terms Full Path and Absolute Path will be used synonymously in any class materials.

4 Examples Of Using Relative And Absolute (Full) Paths The sample directory structure displayed in the below image will be used to list some usage examples of relative and absolute paths. Each rectangle in the below image represents a directory. The directory name is displayed in black and in all capital letters. The text displayed in red and in lower case characters represent files that exist within the respective directory. C:\ MYSTUFF BCC HOME CIS53 CIS31 FINANCE RECIPES DOCS tax return 01.xls mom's meatballs.rcp schedule.doc tax return 00.xls goodsoup.rcp labels.doc FALL01 SPRING02 SPRING01 SPRING00 syllabus.doc syllabus.doc ndsdocs.doc nds notes.doc compad.doc hmwrk1.doc scripts.doc spring syllabus.doc 1) Absolute or Full Path to goodsoup.rcp: C:\MYSTUFF\HOME\RECIPES\GOODSOUP.RCP 2) Absolute or Full Path to compad.doc: C:\MYSTUFF\BCC\CIS53\FALL01\COMPAD.DOC 3) Absolute or Full Path to nds notes.doc. Because the file name does not conform to the 8.3 format, when referencing the path at a command prompt, it must be enclosed in quotes. File names that don t conform to this format are referred to as long file names. (Note: 8.3 format refers to the maximum number of characters in the file name and in its extension; 8 being the maximum number of characters allowed in the file name, and 3 being the maximum number of characters allowed in the extension.) C:\MYSTUFF\BCC\CIS31\SPRING00\NDS NOTES.DOC 4) Absolute or Full Path to schedule.doc file: C:\MYSTUFF\HOME\DOCS\SCHEDULE.DOC

5 5) Absolute or Full Path to tax return 01.xls. (Quotes need on long file names.) C:\MYSTUFF\HOME\FINANCE\TAX RETURN 01.XLS 6) Relative Path to the labels.doc file from C:\HOME DOCS\LABELS.DOC 7) Relative Path to the compad.doc file from C:\MYSUFF BCC\CIS53\FALL01\COMPAD.DOC 8) Relative Path to the spring syllabus.doc file from C:\MYSTUFF\BCC CIS31\SPRING00\SPRING SYLLABUS.DOC 9) Relative Path to the hmwrk1.doc file from C:\MYSTUFF\BCC\CIS53\SPRING02 HMWRK1.DOC 10) Relative Path to the goodsoup.rcp file from C:\MYSTUFF\HOME\FINANCE (With leading periods and a backslash, you re traversing backwards up the directory structure. Two leading periods move you back one subdirectory. In this example, the two leading periods move you up to the HOME directory.)..\recipes\goodsoup.rcp 11) Relative Path to the scripts.doc file from C:\MYSTUFF\BCC\CIS31\SPRING00..\SPRING01\SCRIPTS.DOC 12) Relative Path to the ndsdocs.doc file from C:\MYSTUFF\HOME\FINANCE (Three leading periods move you back two subdirectories. In this example, the three leading periods move you up to the MYSTUFF directory. ) \BCC \CIS31\SPRING01\NDSDOCS.DOC