Using UNIX

a brief introduction

UNIX is an operating system. It likes to use short two-letter commands for most things. When you ask it to do stuff, it doesn't usually prompt you to make sure you're sure. It also doesn't print much back at you unless there's an error.

Most UNIX commands take arguments which are specified after the command -- often with a "-".

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. Subdirectories are marked with a "/".

ls -l gives you the long version of the above. You get the dates the files were created, their sizes, and plenty of other stuff that won't be important.

ls -a lists all the files in a directory. Filenames which start with ".", so-called dot files, are not printed otherwise. Dot files usually contain configuration information for various programs.

ls name lists the contents of the named directory.

cp name new-name copies 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.

cat name prints the contents of name. You can give cat multiple files, and their contents will be concatenated together and output. This is the mnemonic for this command (concatenate).

head name prints out just the first 10 lines of name. This is handy if want to remind yourself of what a file contains. head has many other options; see the man page (see below).

Looking at files

The best way to look at a file (short of firing up an emacs session), 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.

Using the shell

The shell is the command interpreter that you interact with in an xterm. On the mscc machines, you'll be using a shell called tcsh. You can re-run the 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

You can also re-edit previous commands by using the arrow keys to scroll through them. The MSCC machines seem to be set up in such a way that this isn't completely straightforward. Type bind emacs to make it work intuitively. Put this line in your .cshrc to have it be run automatically for you at every login (.cshrc contains commands that will be run whenever a new shell is started).

On-line help

On UNIX, every command has an on-line manual entry, which is a very terse but complete description of what it does. Access these entries by typing man command. You can also use apropos substring to get a list of commands which contain a given substring.

Printing

To print text files in UNIX, use enscript. Specify the printer with the -P flag, and use -2r to save paper. I also use -G to get the "gaudy graphical" look. I'm not sure which printer the output will go to. To find out, type the command printenv PRINTER and show the output to a lab staff.

Setting Defaults

The .cshrc file contains a list of commands that are run every time you start up a command prompt. It is located in your home directory (remember that you need to do ls -a to see files that begin with .).

Conclusion

Those are the most basic basics. This should tell you what you need to know to get through these assignments. For the most part, you should be working within emacs, which I've documented elsewhere. Feel free to ask questions if you have questions about UNIX that aren't covered here.