Command line tutorial

[[Category: Dreamhack]

Help! My Dreamhack has a command line!

If you've never used a Unix-based operating system before, the command line can be intimidating. Fear not! Working with files and data on the command line is actually fairly easy, and once you get used to it, you'll wonder how you ever lived without it.

The key thing to remember in unix commands is that they date from the days when vowels were an endangered species they are often shortened, contracted, or otherwise non-obvious at first glance. This is to make them easier to type -- the general theory is that it's nicer to type 'ls' sixteen thousand times a day than it is to type 'list'. They're generally designed to be typed quickly on a QWERTY keyboard.

Connecting

The window where you connect to your Dreamhack and type commands is also known as a 'shell window', for reasons that don't need explaining at this juncture in time. In order to connect to your Dreamhack, you'll need a program capable of doing SSH (Secure Shell) connections. For Windows, the best program is PuTTY. If you're on a Mac you won't need a separate program; the Terminal (Applications/Utilities/Terminal) will let you connect.

Directories

Everything in Unix is either a process (a running program), a file, or a directory. Files live in directories, which can themselves contain directories, and so on.

When you first log into your Dreamhack, you'll be in your home directory. This is a special directory that stores all of your files and folders, and serves as the root for a lot of commands if you don't otherwise specify an argument. Your home directory is also known as "~" for short.

On the Dreamhack system, your home directory is located in /dreamhack/home/8XXX-yourusername. For instance, if my Dreamhack username is 'dh-rahaeli', and my assigned number is 8083, my home directory is located at /dreamhack/home/8083-rahaeli.

Directory paths are given with slashes separating the directory tree -- each slash represents another directory down the tree. If the directory path starts with a slash, it is an absolute path: it's counted from the root of the machine, the directory that holds all other directories. If a directory path doesn't have a slash before it, it's a relative path, and is usually counted from the directory you're in at the moment. (There are some exceptions to this, but I'll get into that in a bit.)

Command prompt

The command prompt is where you type in what you want the system to do. On a Dreamhack, it looks like this:

dh-rahaeli@hack:~$

Breaking that down into component pieces, it's: your username @ the machine you're on : (your present working directory). So, if you're in the ~/dw/cvs/dw-free directory (and remember, ~ means your home directory, so in this case it's shorthand for '/dreamhack/home/8083-rahaeli'), your prompt will look like:

dh-rahaeli@hack:~/dw/cvs/dw-free$

It's useful to have a long command line like that, because it'll remind you where you are, who you're logged in as, and what directory you're in. (Those of us who often have five or six shell windows open all the time, to various machines, sometimes get lost.)

Listing files and directories

To list files:

ls

This returns all the files in a directory, formatted like this:

dh-rahaeli@hack:~$ ls
README  apache  bin  crontab-import  dw

On Dreamhacks, the output is color-coded, so directories are blue, executable files are green, and plain files are white. (More about permissions and the difference between executable and non-executable files in a bit.)

Outside Resources

Good tutorials on Unix/Linux work:

• http://www.ee.surrey.ac.uk/Teaching/Unix/