Using UNIX

a brief introduction

Introduction to UNIX

UNIX is an operating system. One interacts with UNIX from a program called the "shell". Many UNIX commands are short two-letter abbreviations, such as "ls" for list and "rm" for remove. Most commands do not usually ask you for confirmation, so be careful, especially when deleting files. Most UNIX commands do not print messages back at you unless there's an error. Finally, the behavior of many UNIX commands can be modified by a set of options which are specified after the command, and options usually begin with the "-" character.

File basics

The current directory is called ".". The parent directory is referred to as "..". Your home directory can be referred to using "~". The root directory in UNIX is simply called "/". Files can be specified using slashes between directory names. For example, I can refer to a file named foo in my home directory as "~/foo".

Paths that start with "~" or "/" are absolute pathnames because they refer to a specific starting point. Other paths are relative, and constructed starting from the directory you're in. The example above was absolute and will work no matter where I am. In contrast, "../foo" will go back one level from the current directory and look for foo.

pwd prints the working directory you're in.

cd name changes you into the the named directory.

ls lists the files in the current directory.

ls -l gives you the long version of the above. You get the dates the files were created, their sizes, and other information about permissions to access the file.

ls -a lists all the files in a directory. Filenames which start with "." are not printed otherwise.

ls name lists the contents of the named directory.

cp name new-name copies (duplicates) a file to a new name or location.

mv name new-name moves a file. If new-name is a directory, the file will be moved to that location. If it is a filename, it will be renamed to that name.

rm name removes a file (No warning!).

mkdir name makes a new directory.

rmdir name removes a directory.

Viewing and editing files

The best way to look at a file is to use more. This will display the file one screenful at a time. Between screens, you can hit q to quit, RETURN to advance one line, or SPACE to advance to the next screen. You can also search for text using /text-RETURN.

The best way to edit a file is to use emacs. See the Emacs Intro page for details.

Using the shell

The shell is the command interpreter that you interact with in an xterm. On the CSE instructional machines, you'll start off with a shell called csh. An improved version of csh called tcsh is also available. You can re-run your previous command using !!. You can re-run a command starting with a particular substring using !substring. You can see a list of the recent commands you've typed using history.

If you're using tcsh, you can re-edit previous commands by using the arrow keys to scroll through them. Tcsh has many other useful features, see the manual page for details.

On-line help (manual pages)

On UNIX, every command has an on-line manual entry, which is a very terse but complete description of what it does.

man command-name prints the manual page for a command. The manual page describes all the available options and their behavior.

apropos substring lists those commands whose description contains the given substring.

Telnet/rlogin

You can get access to other UNIX machines remotely using telnet machine-name or rlogin machine-name. For example, to access the remote machine named "saul.u.washington.edu", you would use rlogin saul.u.washington.edu. If your user name is different on the remote machine, you can use -l username to specify what your name is there.

Printing

To print text files in UNIX, use enscript. Specify the printer name with the -P flag, and use -2r to save paper. You can also use -G to get the "gaudy graphical" look.

Conclusion

Hopefully, this should tell you what you need to get started. Much of the work for your homework assignments will be done using emacs and spim, both of which are documented elsewhere. Feel free to ask questions if you have questions about UNIX that aren't covered here.