Unix Commands PowerPoint Presentation developed for LS 560 Information Technology online class - University of Alabama by Debey Sklenar TENacious Cohort ©2014

1 – Login or ssh Being logged in to the server through a shell allows you to see what is happening on a deeper level than you can with a GUI. You have more control than you typically do with a graphical interface.

2 – List Folders or ls command The ls command lists all the files and directories in the directory you are currently in. This is important because computers use a hierarchal directory structure to organize files.

3 – Change Directory or cd command The cd command lets you change directories from one into another. It is important because without it you would be stuck in the root directory and not be able to do anything in other directories.

4 – Move Back or cd.. command The cd.. command lets you back up one level in the directory. Useful for moving around, especially if you have worked your way down in directories and do not need to go back to the beginning.

4a – Return Home or cd ~ command The cd ~ command takes you back to the beginning directory. To illustrate this, I created several levels of test directories. This lets you go back to the start without having to back up one step at a time.

4b – Return Home or cd command However, the class video showed a cd command (no ~) that when tested, looked like it worked the same as the cd ~ command, taking me back to my home directory, illustrated above.

5 – Make New Directory or mkdir command The mkdir insertnewnamehere command lets you make a new directory. Useful because you may need a new directory in which to place new files that do not fit into other established directories.

6 – Change Directory or cd command The cd command can be used to move into other directories, such as the newly created directory. Extremely useful as you will probably want to accomplish something within the new directory.

7 – Display Last or history command The history command shows you the last several commands you've entered. Extremely useful in going back to see how you may have gotten yourself to where you currently are.

8 – Date command The date command will display the current date, time and year. This could potentially become important if the timing on your computer is off; the date command would show you.

9 – Users Logged In or who command The who command tells you who else is currently logged into the server and their login location. If others had write privileges to the same files, it may be useful to see if any of them might be trying to make alterations as well. *Note that here, I am one of 6 users logged into the server. (For some reason, it is showing me twice...)

10 – Calendar or cal command The cal command will display the current month's calendar. Again, this could be useful if your computer (or you) have lost track of time.

11 – rmdir command versus rm -r command My husband advised me to use the rm -r command in order to delete the directory I created in slide 5. (I will illustrate why in the next slide.) Removing a directory can be useful if it is no longer needed.

11a – rmdir command versus rm -r command The difference between the rmdir and rm -r commands is that the rmdir command will only delete a directory that is empty. If you need to delete all the contents as well as the directory, you should use the rm -r command.

12 – Long List or ls -l command The ls -l command will show you a more detailed list of the files found in a directory, such as permissions, date created, and file size. Important for determining what you or others may or may not do with a file.

13 – Directory Permissions From the same slide, note the letters d, r, w, x, and symbol - to the left of the long listing of directories/files. These symbols (called symbolic notation) tell you what you may and may not do (or what rights/permissions you have).

13a – Directory Permissions The letter d stands for directory and is sort of the exception in our permissions because it does not represent any permission granted or denied, but rather the fact that the item listed is a directory rather than a file. If it were a file, you would see a -. It is always the first character.

13b – Directory Permissions The letter r stands for read and appears if reading is permitted. The letter w stands for write and appears if writing is permitted.

13c – Directory Permissions The letter x stands for execute and appears when execution is permitted. The character - appears when no right for a certain attribute is permitted.

13d – Directory Permissions Note the groupings and positions of the letters and - symbol as well. The first set of 3 characters after the initial slot denotes the user class, most likely the account owner.

13e – Directory Permissions The second set of 3 slots is reserved for the group class rights. The third set of 3 characters displays permissions granted to others. This is anyone and everyone with any kind of access.

14 – Globally Search a Regular Expression & Print or grep command The grep command will search out and list (or “print”) on the screen. Here, I searched for !-- on the index file of my website. This can be extremely useful when looking for something, but you are not quite sure of its location.

15 – Log Out or exit command The exit command will log you out of the system. This is best practice and common courtesy. Also, it keeps others from inferring you are working with the system when in fact you are not.

16 – Processes or ps command and ps aux command The ps aux command shows all the processes running on your machine, while the ps command will only show the processes running in your terminal window. Note the end of the ps aux list above followed by the short ps list.

17 – Display a Plain Text File or more command The more +filename command will display that file in your terminal window. This only works for plain text files, however, and if the file is too large to show in its entirety, as above, you can use the space-bar to page down through it.

17a – Display a Plain Text File or more command The problem with the more command is that once you have reached the end of the file, there is no way to get back to the top again. It is still useful to be able to look inside a file. However, there is another way...

18 – Display a Plain Text File with the less command With the less +filename command, a plain text file will still display in your terminal window, but here, you are able to scroll down or up with the arrow keys. I am told this is why...

less is more

Why is Mastery of the Command Line in Unix Important for Information Professionals? The GUI is user-friendly and easy to use, but what if the user is unable to find the information they seek because the GUI programmers did not anticipate such a need from the user? Information Professionals need to be able to “look under the hood” of the GUI in order to determine where the breakdown in need is arising and to help solve the problem.

Unix Commands PowerPoint Presentation developed for LS 560 Information Technology online class - University of Alabama by Debey Sklenar TENacious Cohort ©2014