Using the Command Line

A computer terminal allows the user to enter data into and display data out of a computer. The command line is where a user can issue commands into the computer from the terminal. Your computer terminal can be accessed very simply by searching for 'terminal' in your Mac OS X or Linux system. The commands typed into 'terminal' are case sensitive.

Using the command line within the computer terminal is required extensively when using the #k@ program. If this is your first time using the computer terminal, have no fear! Here we will discuss several fundamental commands that may be necessary for you to use in the #k@ program, and that are also essential to know when working in a computer terminal.


A terminal used a hierarchical structure, starting at the home directory and branching 'downward'. The path is the file's address within the system.

Let us assume the home directory contains two directories (or folders), directory_A and directory_B, and each directory has a sub-directory, sub_directory_A and sub_directory_B, and each sub-directory has one file in it, called file_A and file_B. Then the path of file_B is:


Home symbol (~)

Note that ~ is the symbol for the home directory.

To display to the screen the path of the directory you are currently working in, enter the following command:


List of Files and Directories

To output to the screen a list of files and directories within the current working directory, simply enter the command:


Change Directory

One navigates to a different directory using the cd command. Typing the following will move you to the 'home' directory:


To open a directory one level down from the directory you are in, type cd directory_name.

Typing the following will move you into directory_A from the home directory:

cd directory_A

Typing the following will move you to the directory one level up:


If you wish to navigate to a directory not in your current path (i.e. from sub_directory_B to sub_directory_A) type the path:

cd ~/directory_A/sub_directory_A

Create a File

You can create a file using the command touch. Entering the following command will create the file new_file:

touch new_file

Create a Directory

A directory is created using the mkdir command. Entering the following command will create a new directory directory_C:

mkdir directory_C

Remove a File

One removes a file from the current working directory using the rm command.

rm unwanted_file

Remove a Directory

One removes a directory and all its contents with the rm -r command. The following command will remove the directory unwanted_directory:

rm -r unwanted_directory


One may move a file with the mv command. To move a directory use the mv -r command. The command is mv present_location new_location. The two locations are separated by a 'space'. In the end, the file will be in the new location and NOT in the former location.

Let's try it out!

Using directory_C in the home directory, let's create file_C in directory_C then move it to sub_directory_A:


cd directory_C

touch file_C

mv ~/directory_C/file_C ~/directory_A/sub_directory_A/

To see if you have been successful, you may go to the old and new directories and list their contents.

Copy a File

A file is copied using the cp command. As with move, to copy you enter the file's current location followed by the desired location. Let's copy file_B into sub_directory_A. In the end the file copied will be in BOTH locations:

cp ~/directory_B/sub_directory_B/file_B ~/directory_A/sub_directory_A/

Copy a Directory

A directory is copied using the cp -r command in the same way one copies a file.

cp -r ~/directory_C/ ~/directory_B/

Open a .tar File

To open a tar file in Mac OS X, type the command:

tar -xf filename.tar

To open a tar file in a Linux system, type the command:

tar xzvf filename.tar.gz

Install a file

For Mac OS X we recommend installing Homebrew to install programs. Once Homebrew is installed, the command is:

brew install filename

For debian Linux machines such as Ubuntu, files may be installed by typing:

sudo apt-get install filename


sudo is a Linux command that tells the terminal to make a change that requires administrator approval. In most cases, you (the user) are the administrator. The terminal will prompt you for your sudo password if required. Enter it and proceed.

Enabling a Text Editor

One may modify the contents of a file using a text editor. There are numerous text editors available for use, but if it's your first time using a text editor, we recommend using the nano text editor, simply because it is one of the more basic text editors. You can use nano to edit a file in your current working directory by simply typing in the command nano followed by the name of the file you wish to edit.

Entering in the following command will allow you to edit file_A (assuming you are in the directory where file_A is located):

nano file_A


After Gnuplot is installed, to set parameters for your plot, i.e. title, type:

set title desired_title

Then to the data, simply type at the beginning of the line plot, for example:

plot desired_file_name

You should be in the same directory as the data file you want to access. The exact commands are listed in the tutorials.


To save time when using the command line, press tab to finish the name you are typing, or use the up or down directional arrows to use previous commands into the command line.

You can find more information on using the command line here.