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Once we know the current directory in which the commands are execute, How do we change it? Or more precisely, How can we reference files and folders in the interpreter?

Linux organizes files and folders in a tree-like structure. A file is always in a folder, and a folder may contain files and subfolders. The top level folder in this hierarchy in Linux has the name “/”. Beware of the inclination in this bar because the symbol “\” has a different meaning.

Every file or folder has an absolute path which is the sequence of folders traversed from the root separated by the symbol “/” and terminating with its own name. For example, /dirA/dirB/dirC/file.txt is the absolute path for the file.txt stored in folder dirC itself contained in the dirB folder, itself contained in the dirA folder which is stored at the root of the system. The konsole program that opens the window with the command interpreter is configured to show the absolute path of the current directory on its title bar as shown in Figure 13.1.

A folder is assigned to any user in Linux to store all his/her files. The interpreter abbreviates the path to that directory by the symbol “~”. The ls command with no additional data lists the files in the current directory, but if given the name of a folder after the command name, it shows the files on that folder. Thus, the command ls ~ shows the files in the user folder.

Aside from the files and folders created by the user or programs, every Linux folder has two subfolders defined by default:

These folders are regular folder in all contexts, and therefore can be used in paths. For example, the path /dirA/dirB/dirC/../file2.txt refers to the file stored in the dirB folder because from dirC the folder .. refers to its predecessor, dirB. The following figure shows how this path is interpreted as well as the effect of the “..” and “.” folders.

Figure 13.2.  Absolute path containing “..”

As a consequence of the existence of the “.” and “..” folders, a file may have several equivalent absolute paths. For example, the following absolute paths all refer to the file.txt of Figure 13.2: /dirA/dirB/dirC/../dirC/file.txt, /dirA/dirB/dirC/./././file.txt, /dirA/dirB/dirC/../../../dirA/dirB/dirC/./file.txt, etc. Use the ls to show on the screen the content of the folders in the levels above your current directory up to the root folder.

The absolute path unequivocally identifies any file or folder in the system, but it may be very large and therefore inconvenient to type as part of a command in the interpreter. The alternative is to use relative paths.

A “relative path” is a sequence of folder names separated by the “/” symbol not starting by “/” (otherwise it would be an absolute path) that is interpreted using the current directory as prefix. Assuming that the current directory in the interpreter is dirC, the following figure shows the interpretation of different relative paths. Note that none of these paths starts with “/”.