Login

• Your user id is your standard College account, 4 letters from your last name and 4 digits.

• Your password is the string "just2day" (without the quotes, of course!). Change it at once with the yppasswd command (see below).

• Your HOME directory, /home/<userid> or ~ for short, will appear to contain only the directory Desktop.

Now what?

Once you have logged on, you will see your desktop. It will be more or less as you left it, no matter which of the Linux systems you login from. You will want to open a Console, or a UNIX Shell (known also as an xterm, or X-terminal) in order to enter commands to the command-line interface, or the shell.

Setting your password

• Unix/Linux used to use the command passwd to change passwords, but since many systems, including ours, use the Network Information System (NIS) formerly known as the "Yellow Pages" for network-wide password control, you will use the command yppasswd.

  Anyone who does not set their password within the first lab will have their account deactivated by the sysadmin.

  
  

• Your password should contain both letters and digits, and even punctuation, and must be at least 6 characters long. Ideally, you will mix upper and lower case letters.

The vi text editor

Knowledge and skill in using the vi editor is a required component of this course. Please read pages 71-72 in "Practical Linux" and pages 301-302 in "Linux Shells by Example" for some information about vi. There's more information in this document, and in the man page for vi (man vi or man vim).

Questions about vi may appear on tests and exams.

Finding information about Linux

In addition to your textbooks, you should learn how to use the man command to read the manual pages that are online on all Linux and Unix systems. Some systems will have additional online documentation, but all have man pages. Enter the command below to get started:

man man

Basics of the Bourne-Again-Shell (bash)

Reference: Chapter 8 of "Linux Shells by Example"

In Unix and Linux, "shell" is the term used to describe the command-line interpreter (roughly equivalent to command.com in DOS). In this course, we will use the bash shell because of its wide popularity on Linux, although there are other shells available such as tcsh, sh, ash, and more.

Getting started

History Mechanism (like doskey in DOS)

A few commands to start with

General notes

• Linux is case sensitive. For example, the file names Demo.file and demo.file are completely different files in Linux and can both reside in the same directory without conflict.

• This case sensitivity also applies to usernames, passwords, command names, and so on. Take care with CapsLock: the commands cc and CC are not the same.
  This is also the likeliest common problem in failing to login successfully.

• In Linux, the concept of "drives" as in Windows does not apply. There is no C:, or even an A: mountable drive. The entire file system appears as one volume (even when it spans multiple hard disks or a network). Any directory (or folder) can be addressed by a pathname originating at the root directory "/", your HOME directory "~", or from the current working directory "." or its parent directory "..".

• Linux is designed for multi-user, multi-tasking, network-based operation, so a user's HOME directory is typically more important to them than the system's root or other system directories.

• Linux uses long file names (255 characters maximum), and the dot character has no special meaning in a file name. As a result, you can easily have filenames with many dots in them, such as demo.file.version.1.

• Linux has no concept of a file extension (such as Microsoft Windows uses) built into the operating system. Some applications will use extensions such as .c, .o, .tar, and .gz, mostly for your convenience. Executable files, including programs, do not normally end with a .exe extension.

• The forward slash / is used to separate directory names in a path instead of the backslash
  character \ that is used by all the Microsoft operating systems including Windows.

• Command options are normally placed immediately after the command name. Each option is prefixed with a dash - character, and options can often be either combined or separated (that is, xxx -a -b and xxx -ab or even xxx -ba are usually equivalent ways to invoke some imaginary command xxx with options a and b).

Some useful UNIX commands to get started

Command	Meaning
ls	List the names of the files in the current directory
ls -l	List the files in long format, with additional detail
mkdir demo1	Make (or create) a new directory named demo1
rmdir demo2	Remove (or delete) the directory named demo2
cd demo3	Change the current working directory to demo3
pwd	Print the name of the current working directory to the screen
cd	Change the directory to the user's own HOME directory
cp A B	Copies the file named A to the file B, creating a new file if needed
mv C D	Move a file or directory to a new location, or simply change its name
rm E	Remove (delete) the single file E
rm *	Remove every file in the current working directory (be careful)
mv F G	Rename the file or directory F by moving it to the new name G
vi H	Use the visual interactive editor (see below) to edit file H
gcc -c src.c	Compile the file src.c with the GNU C compiler without linking

Fifty or so general Linux commands (and other things)

The commands listed below are ones that you will use throughout the term. You must become familiar with each command and its main options.

Informational commands

File editing commands

File and Directory manipulation commands

File and Filter commands

Input/Output (re)direction (and things)

Miscellaneous commands (and things)

Editing text files

Although there are many editors and word processors available for Linux, the vi visual editor is the standard editor that is available on every Unix and Linux system. You may find vi difficult to learn and use at first, but you will come to appreciate its many powerful features.

The version of vi often found on Linux systems (including ours) is a derivative named vim
(vi improved)invoked by typing either vi or vim at the command prompt.

The key to using vi is to remember that it was developed before cursor controls like the arrow keys, Page Up/Down keys, and other editing keys were commonly available on keyboards. To work around this, all forms of vi define three basic operating modes:

• text insertion (input mode; characters go in as text);

• cursor movement and simple editing (command mode; characters are executed as commands);

• sophisticated editing operations (line edit or ex mode using the bottom line of the screen).

Therefore, each key on the keyboard can have three entirely different meanings, depending in which mode the editor receives it. Remember: Upper-case and lower-case letters are different commands! Try both p and P for pasting, for example, in command mode.

When you first start vi, you are in command mode. Press i to enter text input mode and type your material. Return to command mode by using the ESC key to end insert mode. Make changes or corrections from input mode as needed. When you are finished, go to edit mode to save your file and exit. Use :w to write your file to disk, or :w <filename> if it needs a new name, and :q to exit. You may combine :w and :q as :wq for speed.

The diagram below illustrates methods of moving between each mode, and some of the keys available in each mode.

Some basic commands for vi

These basic commands are enough to get you started and to complete most simple editing tasks. The more commands you learn, the faster you will work.

Adding new text (from command mode into insert mode)

Moving around without the arrow keys (within command mode)

Editing text (from command mode)

Search and Replace (from ex mode)

Save and Exit (from ex mode; you can also use ZZ in command mode)

You will often find vi commands in other places as well, either derived from vi itself or often from a common ancestor program. For example, the / and ? search commands work in more and man, and a close relative of :s works in sed.

The use of h, j, k, l is guaranteed to move the cursor on all compatible editors derived from vi, but many implementations including vim now also support the arrow keys on the PC keyboard (both the "inverted T" and the keypad when NumLock is off).

Program Debugging

Your programs, both C-language and shell scripts, will not work perfectly the first time (a great surprise to you, I am certain). Many people use print statements of the appropriate flavour to debug their programs, a barbaric practice suitable only for the most trivial of programs.

Real programmers use professional debugging tools whenever possible.

Source-level bash code debugging

The bash shell can display each line before or after all substitutions, or merely check the script syntax. Tracing can also be turned on and off inside a script:

Command	Option	What it does
bash -x scriptname	Echo option	Display after substitutions
bash -v scriptname	Verbose option	Display before substitutions
bash -n scriptname	Noexec option	Check syntax
set -x	Turn on echo	Start trace
set +x	Turn echo off	Stop trace

Source-level tcsh code debugging

Including -x on the first line of the shell script will cause the csh program to provide a certain amount of diagnostic output at the source level, but no interactive debugging tool is provided. You will have to place input statements (to pause execution) and output statements (to display certain diagnostic values) in addition to the execution trace.

You can also temporarily add the debug option by entering:

tcsh -x name_of_script [list of arguments]

More sophisticated scripting tools, such as Perl, have more sophisticated debugging tools.