IT 244: Introduction to Linux/Unix

IT 244: Introduction to Linux/Unix
Class 4

Microphone

Questions? Issues?

Does anybody have any questions before I begin?

Homework 2

I have posted homework 2.

As usual, it will be due this coming Sunday at 11:59 PM.

Today's Class

Today I will talk about certain characters that have special meaning on the command line.

I will also discuss some of the most important Unix utilities.

General Advice

Make a Study Schedule

One of the most important thing you can do to do better in class ...
is to make a study schedule ...
and keep to it
A consistant study routine is the single most important thing you can do ...
to improve your grade
You should set aside regular chunks of time for this course ...
and stick to it as best you can
The semester is long - 14 weeks
Most of you have many responsibilites
Conflicting demands on your time can cause you to lose focus
Having a regular schedule can keep you on track ...
and prevent panic attacks before exams
Time is a finite resource
Once you have wasted an hour ...
you can never get it back
If you find your schedule is not working ...
make some changes
But do not use that as an excuse to abandon a schedule
There is an old saying
If you fail to plan ...
you are planning to fail

Course Work

First Graded Quiz

The first graded quiz will be given on Tuesday next week
The question on the quiz are taken from the ungraded quizzes ...
of the previous week
You should expect a Graded Quiz each week on Tuesday
If you do not take the quiz when it is offered ...
you cannot take it at another time
If you miss a quiz but have an excuse, send me an email

Gradescope

In order to receive your scores in Gradescope ...
you need to sign in to my Gradescope section
You do not have to register with Gradescope
In the next few days I will enter all your UMB addresses into Gradescope
You will then receive an email from Gradescope
What happens next depends on whether you are already registered with Gradescope
If you are new to Gradescope
- Click the "Set your password" link
- Confirm your password
- Click Save
- You will then be taken to the page for your course
If you are already registered with Gradescope
- Click the link to the course
- At the login screen enter your UMB email address and your Gradescope password
- If you have forgotten you password, click the "Forgot your password"link
You will find more information about Gradescope here.

Tips and Examples

Use Flash Cards to Prepare for Graded Quizzes

To prepare for the Graded Quizzes you need to study the Class Quiz answers for the previous week
The best way to do this is to use flash cards
You take an index card and write the question on one side and the answer on the other
You should make a set of flash cards for each class
Label them with the Class Number and put a rubber band around them
Keep these cards after the graded quiz
You will need them for studying for the Midterm and Final
I made flash cards when taking courses for my Masters degree
I went through them on my way to class on the T
There are programs that you can use to create virtual flash cards
But the simple act of writing each card helps you remember the material

Always Check Your Work

It is easy to make a mistake when writing scripts
That's why it is very important to check every script you write
Doing this is easy for the Class Exercises
I have created scripts to test the scripts you write for each Class Exercise
You can use them too
You will find them in the directory ~ghoffman/it244_test
But you cannot go to that directory to run the script
To run the scripts use the pathname at the bottom of each Class Exercise
To run the test script for today's Class Exercise use
```
~ghoffman/it244_test/ex04.sh
```
Enter your Unix account name when prompted

Recorded Class Meetings

All lectures for this class are recorded
Use this resource if you miss a class ...
or don't quite understand something mentioned in class
You will find links to the recordings of class meetings here

Review

The Unix `script` Command

The script command creates a transcript of your Unix session
It records everything you type on the command line ...
and all the output the command creates
By default, script creates a text file named typescript in your current directory
Running script a second time will overwrite the previous typescript file
To prevent this from happening run
```
script -a
```
With the -a option, script will add to the previous typescript file ...
so you won't lose your work
When you have finished with your script session you must type "exit"
Otherwise you will lose the entire session

Correcting Mistakes on the Command Line

You can correct mistakes on the Unix command line
This is called command line editing
Use the following Control key combinations
- Control A - Move the text insertion point to the beginning of the command line
- Control E - Move the text insertion point to the end of the command line
- Control K - Remove everything from the text insertion point to the end of the line
- Control U - Remove everything from the text insertion point to the beginning of the line
- Control Y - Pastes back on the command line what was removed with either Control K or Control U
The Left and Right arrow keys, ← and → move the text insertion point

Retrieving Your Last Command Line Entry

To retrieve the previous command, hit the Up arrow key, ↑
You can do this several times to go back to any previous command
The Down arrow key, ↓ takes you in the opposite direction

Stopping a Running Program

You can abort a running program using Control C

Getting Help with Unix Commands

Many Unix utilities have a help option
The help option provides some basic information about the command
Some commands use -h as the help option
But most use --help
For more information, use man or info
Follow man or info with the name of the command

Attendance

New Material

Special Characters

There are some characters that have special meaning ...
on the command line
You should avoid using them as arguments to commands

They are

& : | * ? ' " [ ] ( ) $ < > { } # / \ ! ~

Three other characters, called whitespace, are also special
The whitespace characters are
- Space
- Tab
- Newline
Spaces are used to separate entries on the command line
```
	
ls -l dir1
```
They separate the command from its options and its arguments
Tab has a special meaning we will discuss in another class
The newline character is what you get when you hit Enter on a PC ...
or Return on a Mac
When you are typing in a text editor ...
the newline moves you down to the next line
Hitting Enter or Return on the command line ...
tells the shell to run the command you have entered

Quoting and Escaping

Sometimes you might need to use a special character in an argument ...
to a command
In that case, you must do two one of two things
- Use quotes
- Escape the special character
Escaping means putting a backslash, \ , in front of a special character
This turns off the special meaning of the character
The backslash must come immediately in front of the special character
The echo command prints whatever comes after it
It is used in scripts to print a message to the user
```
$ echo Hello World!
Hello World!
```
Here's what happens when I try to use echo with the special character ~
```
$ echo ~
/home/ghoffman
```
You'll learn what ~ means in a future class
I can use ~ with echo if put a backslash in front of it
```
$ echo \~
~
```
You can use quotes to do the same thing
```
$ echo '~'
~

$ echo "~"
~
```
There are two types of quotes
Single quotes - ' '
Double quotes - " "
They have slightly different purposes
But you don't need to worry about the difference for now

`pwd` - Show Your Current Directory

You are always somewhere in the filesystem
If you are not where you need to be ...
commands might not work as you expect
You can always find your current location with pwd ...
which stands for print working directory
The command does not take an argument
So a call to pwd looks like this
```
pwd
```
Here is what I see when I run pwd after connecting to pe15
```
$ pwd
/home/ghoffman
```

`cd` - Change Directory

When you first connect to pe15 you will be in your home directory
Usually you will need to go to another directory to do your work
To do this you will need to use the cd command
cd stands for change directory
Unix commands are usually very short ...
to make them easier to type
cd changes your location in the filesystem
A call to cd looks like this
```
cd  DIRECTORY_NAME
```
If I were in my home directory and wanted to go to the tmp directory inside my home directory ...
I would type
```
$ cd tmp
```
If you use cd with an argument it moves you to that directory
If you use cd without an argument it takes you to your home directory
This can be useful
As you begin to work with Unix you may get lost ...
and not be in the directory you need to be
If that happens simply type cd without an argument
That will take you back to your home directory ...
from which you can start again
Sometimes you need to go up the chain of directories
cd can do this if you give it the argument ..
```
cd ..
```
To go up more than one directory use multiple instances of ..
Each .. must be separated by a /
To go up two directories enter
```
cd ../..
```

`ls` - List the Contents of a Directory

ls (list) is one of the most basic Unix commands
It lists the files and directories inside a directory
A call to ls looks like this
```
ls DIRECTORY
```
You can use ls with or without an argument
If you give ls a directory as an argument ...

it lists what is inside that directory

$ ls it244_test
1        ex06.sh  ex12.sh  ex20.sh      ex24.sh     five_lines.txt
1.sh     ex07.sh  ex13.sh  ex21.sh      ex25.sh     script_improvements.txt
ex02.sh  ex08.sh  ex16.sh  ex22.sh      ex26.sh     step_comment_check.sh
ex03.sh  ex09.sh  ex17.sh  ex22_sum.sh  ex27.sh
ex04.sh  ex10.sh  ex18.sh  ex23.sh      ex_list.sh
ex05.sh  ex11.sh  ex19.sh  ex23_sum.sh  exnn.sh

When you don't give ls an argument it lists the current directory

$ pwd
/home/ghoffman

$ ls
bin           course_materials  it116       it244        stdwrk       tmp
bugs          demos             it116_test  it244_test   submitted    wrk
code          haoyu             it117       mail         testing      xrchiv
course_files  html              it117_test  public_html  tests_taken

The command line does not give you much information
It it easy to lose track of where you are
When this happens, certain things will not work as you would expect
Running ls can help you know you are in the right directory
Until you get more comfortable with the command line ...
it's a good idea to use ls right after using cd
If the listing looks wrong, you are in the wrong directory
Like many Unix commands ls has many options
But two are used most often

The -l (el) option gives you a long listing

$ ls -l
total 20
-rw-rw-r--   1 ghoffman       103 Sep 11 14:34 basic.css
-rw-r--r--   1 ghoffman      3560 Aug 29 13:30 emacs_cheat_sheet.html
-rw-r--r--   1 ghoffman       701 Aug 29 13:30 index.html
drwxr-xr-x   6 ghoffman       512 Sep 15 14:11 it_244
-rw-r--r--   1 ghoffman      6831 Aug 29 13:30 tips.html
-rw-r--r--   1 ghoffman      6052 Aug 29 13:30 unix_cheat_sheet.html

We'll talk more about this when we discuss access permissions
Directories can contain files that are used to configure Unix
These files have names that beging with .
Normally you don't see these "invisible" files

If you want to see them, use the -a (for all) option to ls

$ ls -a
.               .bash_profile.bak  .emacs.d  it244    .nano       .subversion
..              .bashrc            .forward  it244.d  .pinerc     test_setup.sh
.addressbook    .bashrc~           it116     it480    .plan       tmp
.bash_history   .cache             it116.d   .local   .plan2      .viminfo
.bash_profile   .config            it117     .login   .profile.d
.bash_profile~  .emacs             it117.d   .msgsrc  .ssh

We'll discuss these files later in the course

`cat` - Print the Contents of a File

If you want to see what is inside a file ...
you can use cat
A call to cat looks like this
```
cat FILENAME
```
cat stands for concatenate ..
and it prints a file to the terminal
```
$ cat foo.txt 
foo
bar
blecth
```

When run with the -n option, cat shows line numbers

$ cat -n numbered_lines.txt 
     1  Line 1
     2  Line 2
     3  Line 3
     4  Line 4
     5  Line 5

If you run cat on a long file, the output can scroll off the screen
To view long files, you should use a paging program
Paging programs show the file one screenful at a time
I'll discuss them more in a future class

`rm` - Delete a File

Sometimes you create a file for some purpose ...
but need to delete it when your work is done
You can delete a file with the rm utility
A call to rm looks like this
```
rm FILENAME
```
rm stands for remove
Do not use rm unless you are sure you no longer need the file
There is no undelete feature in Unix
Deleted files cannot be recovered if not backed up
Don't delete a file unless you are sure you won't need it
To remove all the files in a directory use
```
rm *
```
Be careful when using * with rm
It will delete everything
There is no way to get back what was deleted
If you run rm with the -i option it will ask you before deleting each file
```
rm -i * 
rm: remove regular file `foo.txt'? y [Enter]
```
It's good idea to use this option when running rm *
rm cannot remove a directory unless you use a special option
NEVER USE rm * IN YOUR HOME DIRECTORY
Every semester at least one student does this ...
and loses their it244 directory
I can fix this ...
but it's a pain in the butt

`mkdir` - Create a Directory

Directories allow you to organize your files
You will have to create a new directory for every Class Exercise ...
and homework assignment
You create a directory using the mkdir command
mkdir stands for make directory
A call to mkdir has the following format
```
mkdir DIRECTORY_NAME
```
The new directory will be created inside the current directory

`rmdir` - Delete a Directory

You cannot delete a directory using rm
Instead you need to use rmdir
rmdir stands for remove directory
A call to rmdir has the following format
```
rmdir DIRECTORY_NAME
```
rmdir will not work unless the directory is empty
Before you use rmdir you must ...
cd into the directory to be removed ...
remove all files with rm
```
rm *
```
...
and return to the above directory with cd
```
cd ..
```
Then use rmdir to remove the directory

`cp` - Copy Files

On the command line yoy can make copies of files and directories ...
using the cp command
cp stands for copy
cp takes two arguements
The first is the name of the file or directory you want to copy
The second is one of two things
Either the directory where you want the copy to be made ...
or the name of the new file or directory
To copy a file use the format
```
cp  FILENAME  DIRECTORY_OR_NEW_FILENAME
```
To copy a directory use the format
```
cp -r DIRECTORY  TARGET_DIRECTORY
```

Here is an example of copying a file to a directory

$ ls
dir  foo.txt

$ ls dir # dir is empty. there is nothing in it

$ cp foo.txt dir

$ ls dir # now dir has a copy of the file
foo.txt

Here is an example of making a copy of the file ...
in the same directory ...

with a new name

$ ls
dir  foo.txt		
			
$ cp foo.txt bar.txt

$ ls 
bar.txt  dir  foo.txt

To copy a directory you must use the -r option

`mv` - Move a File or Directory

mv is a command that can do 2 things
It can move a file or directory from one location in the filesystem ...
to another
Or it can rename a file or directory
mv stands for move
To move a file or directory to a different place use the format
```
mv  FILENAME_OR_DIRECTORY_NAME  NEW_DIRECTORY
```

To change the name of a file or directory use the formal

mv  FILENAME_OR_DIRECTORY_NAME  NEW_FILENAME_OR_NEW_DIRECTORY_NAME

In either case, mv takes two arguments
The first argument is always the the name of the file or directory
When used to move, the the second argument is the new location

Here is an example using mv to move a file to a new location

$ ls
foo.txt  it244  work

$ ls work # the work directory is empty

$ mv foo.txt work

$ ls  # foo.txt is no longer where it once was
it244  work

$ ls work # foo.txt has been moved to the work directory 
foo.txt

Here is an example using mv to change the name of a file

$ ls
foo.txt  it244  work

$ mv foo.txt bar.txt

$ ls
bar.txt  hold  it244  work

`man` Page Sections

The files that are shown when we use the man command are called man pages
They are divided into the following sections
- 1 User commands
- 2 Programming interfaces for kernel system calls
- 3 Programming interfaces to the C library
- 4 Special files such as device nodes and drivers
- 5 File formats
- 6 Games and amusements such as screen savers
- 7 Miscellaneous
- 8 System administration commands
Section 1 is the most usefull to ordinary users
But the others can help you learn about Linux
For example, apropos shows more than 1 entry for the passwd command
```
apropos passwd
...
passwd (1)
passwd (5) 
...
```
Running man passwd shows you the section 1 entry ...
which is the command to change your password
But runnin man 5 passwd shows the format of the file /etc/passwd ...
which is one of the Linux files with password data
Don't get too excited about the games section 6
As far as I can tell it only lists two programs
- cowsay
- fortune

The first create a silly character graphic

$ cowsay Hi there
 __________
< Hi there >
 ----------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

The second prints something you might see in a fortune cookie
```
$ fortune
You'll feel much better once you've given up hope.
```
The man pages are stored in /usr/share/man

General Advice

Course Work

Tips and Examples

Review

New Material

Questions? Issues?

Homework 2

Today's Class

General Advice

Make a Study Schedule

Course Work

First Graded Quiz

Gradescope

Tips and Examples

Use Flash Cards to Prepare for Graded Quizzes

Always Check Your Work

Recorded Class Meetings

Review

The Unix script Command

Correcting Mistakes on the Command Line

Retrieving Your Last Command Line Entry

Stopping a Running Program

Getting Help with Unix Commands

Attendance

New Material

Special Characters

Quoting and Escaping

pwd - Show Your Current Directory

cd - Change Directory

ls - List the Contents of a Directory

cat - Print the Contents of a File

rm - Delete a File

mkdir - Create a Directory

rmdir - Delete a Directory

cp - Copy Files

mv - Move a File or Directory

man Page Sections

Class Exercise

Class Quiz

The Unix `script` Command

`pwd` - Show Your Current Directory

`cd` - Change Directory

`ls` - List the Contents of a Directory

`cat` - Print the Contents of a File

`rm` - Delete a File

`mkdir` - Create a Directory

`rmdir` - Delete a Directory

`cp` - Copy Files

`mv` - Move a File or Directory

`man` Page Sections