Basic Command Lines

This README file will teach you the basic command line usage for macOS/Linux. Note that this guide is not comprehensive; if you are interested in more commands, you should search them on google.

The Basics

After opening your terminal, you should see a $. You can then type any command after the dollar sign. The home directory is indicated by ~.

Directories

$ cd [folder]

This will change the current directory to [folder]. For example, if you type $ cd Desktop, you will navigate to the Desktop directory.

Note: if you type $ cd in any directory, you will go back to your home directory.

Quick tip: you can drag a folder to your terminal, and the terminal will copy the folder path to the command line.

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$ pwd

This will print out the current working directory. For example, if you type $ pwd in the home directory, you should see something like /Users/[YourName].

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$ ls

This will list out all the files and folders in the current directory. You can also add -l to list out files/folders in details, or -a to list out files/folders and hidden files/folders.

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$ mkdir [folder_name]

This will create a new folder named 'folder_name'. For example, if you type $ mkdir test in your Desktop directory, you will create a folder named 'test' in the Desktop.

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Files

$ touch [file_name]

This will create a new file named 'file_name'. For example, if you type $ touch hello.txt in your Desktop directory, you will create a file named 'hello.txt' in the Desktop.

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$ open [file_name]

This will open the file whose name is 'file_name'.

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$ cat [file_name]

This will display the file whose name is 'file_name' in terminal.

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Miscellaneous

$ clear

This will clear the terminal screen.

Java

Now, you should have some basic understanding of how to use the command line. Here, I will show you how to run java program in terminal.

First, you should navigate to the directory that contains java file(s). If you use Eclipse to write java program, the java file(s) should be in the src folder. After that, type

$ javac [java file name]                  # this will create a .class file
$ java [java file name without .java]     # this will run the java program

Example:

$ javac Main.java
$ java Main

The javac command will take Main.java as input and output a Main.class, which is in bytecode, and the java command will execute that bytecode.

Quick tip: You can type javac *.java to create all .class files at once.

In addition, you can also add parameters after the java command. For instance, in Lab4, you can type

$ java DNAList <arraysize> <commandfile>    # without the '<' and '>'

Inside the main method, you can use args[0] to access the arraysize and args[1] to access the commandfile.

If you want to terminate a java program, like a running GUI or an infinite loop, you can press ctrl+c to terminate the program.