Most computer systems organize files in a hierarchy of folders or directories. So, for example, a file containing an assignment (called "1st_assignment") might be stored in a directory called "Assignments"; that directory might in turn be stored in a directory called "Music824", which is stored in "Schoolwork". We can represent the full location of the file as:
/Schoolwork/Music824/Assignments/1st_assignmentNotice the use of slashes (/) to separate each of the components in the location. Also notice that the location begins with a leading slash. When a location begins with a slash it is referred to as an absolute location.
Every file in the computer system can be referred to by its absolute location. For example, the following are all absolute locations:
/Universe/SolarSystem/Earth/NorthAmerica/USA/Ohio/Columbus/OSU/WeigelHall
/Filesystem/Username/Directory/Subdirectory/file
/var/opt/Humdrum/Scores/Bach/Brandenburg/bwv1047a.krn
Files and directories can also be referred to using a relative location. On the OSU campus, you can say "I'm going to Hughes Hall" and people will understand what you mean. But if you were in Vienna, no one would understand where you were going. In order to be understood in Vienna, you would have to say, "I'm going to Columbus, Ohio in the United States; and on the Ohio State University campus there is a building called "Hughes Hall." That's where I'm going." On the Unix system, relative locations are evident whenever the leading slash is missing. For example, the following are all relative locations:
OSU/WeigelHall
Username/Directory/Subdirectory/file
bwv1047a.krn
Relative locations are always relative to a working directory. Whenever you use the Unix shell (the window in which you type commands), your window resides in a location on the system. For example, your shell might reside at the following working directory:
/Universe/SolarSystem/Earth/NorthAmerica/USA/Ohio/Columbus/OSU
/Filesystem/Username/
/var/opt/Humdrum/Scores/Bach/Brandenburg/bwv1047a.krn
The ls command lists all of the files and subdirectories in the current directory.
| Command | Action |
| ls | list the files and subdirectories for the current directory |
| ls -l | list the files and subdirectories for the current directory (long format) |
| cd X | change directory to directory named X |
| cd .. | go up one directory level |
| pwd | Present Working Directory -- identify the name of the current directory |
| date | display date and time |
| man X | display manual pages for command X |
| more X | display contents of file named X |
| mv X Y | move a file; i.e., rename the file X (old) to the name Y (new) |
| cp X Y | copy the file named X as the new file named Y |
| rm X | remove a file; delete file named X |
| rmdir X | remove a directory; delete directory named X |
| mkdir X | make a directory; create directory named X |
| pico X | invoke `pico' text editor for file named X |
Useful information regarding UNIX can be found at innumerable web sites. Some useful sources are