What is Linux? Linux is a widely-used command-line operating system. A command-line operating system doesn't provide the fancy graphical interface we're used to (menus, buttons, etc.). Instead, the user has to type in text commands to tell the computer what to do. The commands tend to be short, to save typing, so they tend to seem cryptic to new users. Linux remains popular because some users find it faster and simpler to communicate by means of text than by mouse clicks. It also gives more advanced users the capability to create scripts combining sequences of commands.

Many Linux systems provide a graphical interface to access some of the capabilities of the system, and can run graphical programs such as web browsers. There still remains a command-line system at the heart.

If you want to try a Linux machine at Queen's, go the the CASLab web site and choose "How To...", then "Use Linux".

Linux vs. DOS: If you've used DOS before, you may see some similarities between DOS and Linux. Linux is based on the Unix operating system, which is much older than DOS (or Microsoft itself, for that matter). I'll let you speculate on who might have copied from whom!

Using Linux: I will describe the basics of the Linux command-line system. On some systems, there's a graphical interface. You may be able to find menu entries for some or all of the things you want to do. To get to the command-line, look for a menu entry labelled "terminal" or "console".

Once you're looking at the command line, you should see a "command prompt". The command prompt is usually a single character such as "%" or "$". Sometimes the command prompt will include the name of your current folder. The command prompt means that Linux is waiting for you to type a command. When you type a command, Linux will prompt out the result of the command, then type another command prompt. It's very simple. The only hard thing is remembering the commands to type!

Notes About File Names in Linux:

• When you're working in Linux, you are always "connected" to a particular folder, called your current folder. If you refer to a file without any folder name preceeding it, Linux will look in your current folder.
• DOS uses the forward slash character ("/") to separate folder and file names. For example, if you refer to one/two/myfile.java, DOS will look in your current folder for a sub-folder called one, then look in that sub-folder for a folder called two, then look in that sub-sub-folder for a file called myfile.java
• The special file name ".." refers to the parent of the current folder.
• To give an absolute file name, not starting at your current folder, start your file name with a slash. For example, the file name /myfolder/myfile.java refers to a file in the top-level folder myfolder, regardless of your current folder.
• The "*" character is a wildcard. For example, *.java matches any file name that ends with the characters .java, and CISC*Assn1.txt matches any file name that begins with CISC and ends with Assn1.txt. This is useful for specifying multiple files with similar names. It also saves you from having to type long file names in full.

Basic Linux Commands:

• cd: Change to a different folder. (Stands for "change directory".) For example, cd mydir moves you into a directory called mydir.
• pwd: Prints the name of your current folder. (Stands for "print working directory".) This is useful when you've been changing folders a lot and you forget where you are.
• ls: Displays the contents of a folder. (Stands for "list".) If you type ls followed by the name of a folder, you'll get a list of all the files in that folder. If you leave out the folder name, you'll get a list of all the files in your current folder.
• cat: Types the contents of a file. (Stands for "catalog".) If you type cat Assn1.java, Linux will display the contents of Assn1.java.
• less: This is like the cat command, but geared toward long files that won't fit on the screen all at once. It pauses after every screenful and waits for you to type a space character before it continues.
• rm: Deletes a file. (Stands for "remove".) For example, rm myfile.java will delete myfile.java from your current folder. Be careful with this; Linux has no Recycle Bin!

Warning: Unlike Windows and DOS, Linux is case-sensitive. The commands above must be typed in lower-case. File names may not be recognised if you get the capitalization wrong.