Tips and Examples

• Class Exercises
• Getting Help
• Describing a Problem
• Don't Use Screenshots in Piazza

Review

• Shells
• Unix Commands

New Material

• The Command Line
• The Unix script Command
• The Editor Used in This Class
• The nano Text Editor
• Retrieving Your Last Command
• Correcting Mistakes on the Command Line
• Stopping a Running Program
• Using Options with Unix Commands
• Getting Help with Unix Commands
• The System Manual
• The info System
• Searching for a Keyword with apropos
• Getting Help from the Internet
• Homework Directories
• Using script in Homework 2

Login Failure

If you enter the wrong password 5 times when connecting to pe15 you will be temporarily blocked from logging in to this machine.

This lock out will only last for 2 hours.

After 2 hours, you should be able try again.

If you have forgotten or misremembered your password, you can change it.

Go to https://portal.cs.umb.edu/password/

Recordings of Class Meetings

You will find links to the recordings of class meetings here.

Use of Storage Space on the CS LAN

All of you will have an account on the Computer Science Department network.

With this account you get a home directory.

There is a limit on the total size of the files in your home directory.

So you should not store there anything you do not need for your classwork.

Readings

If you have the textbook you should read chapter 2, Getting Started.

You will find a list of all reading assignments here.

There is a link to this page on the class web page.

Homework 2

I have posted homework 2.

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

Let's take a look at the assignment

Class Quizzes

From now on, each class will have a Class Quiz.

The Class Quiz is ungraded.

It is designed to help you remember the material covered in class.

Here is how it works.

Go to the listing of Class Quizzes you will find here.

Click on the link for the quiz you need to take.

Answer all the questions on a piece of paper.

Go to the listing of Class Quiz Answers you will find here.

Check your answers.

First Graded Quiz

The first graded quiz will be given on Tuesday next week.

The questions from the graded quiz are taken from the ungraded quizzes of the previous week.

Unless I tell you otherwise, you should expect a graded quiz each week.

The quiz will be available on Gradescope on Tuesday.

Do Not Post Anything From this Class Online

There are many web site that claim to "help" students learn new material.

As far as I am concerned sites like Chegg and CourseHero get their money by helping students cheat on their assignments.

Posting ANYTHING on such sites is a violation of your Oath of Honesty and will be reported to the Provost's Office.

This includes quiz and exam questions as well as homework assignments and Class Exercises.

Questions

Are there any questions before I begin?

Tips and Examples

Class Exercises

• There is a Class Exercise for every class ...
• except the review sessions for the midterm and final exams
• Each Class Exercise must be in a separate directory inside the ex directory
• The ex directory must be inside your it244 directory
• If you do not finish the script in class you can finish it later
• All Class Exercises must be finished before the following Sunday at 11:59 PM
• I check your Class Exercises 4 times a week
• The last check is on the weekend after they are due
• If there is a problem with your script, or it is missing ...
• I will send an email to your UMB email address
• If the exercise is not complete or it has an error ...
• you will lose two points for each day it is late
• I have have written test scripts for each of the Class Exercises
• I use these scripts to test your code
• You can run these scripts to test what you have written
• But you have to connect to pe15.cs.umb.edu to do this
• At the bottom of every Class Exercise is the command you run to test your script
• When you run this command you will be asked for your username
• After you enter this an hit return, the test will run
• Here is how it looks for Class Exercise 2

  $ ~ghoffman/it244_test/ex02.sh
  Unix username: ghoffman
  ex  hw
  ex10  ex12  ex16  ex18	ex2   ex22  ex24  ex26	ex5  ex7  ex9
  ex11  ex13  ex17  ex19	ex21  ex23  ex25  ex27	ex6  ex8
  ex2.sh
  ghoffman 		 Glenn Hoffman
  Class Exercise 2

• When you run the test scripts you will not see all the ex directories
• When testing future Class Exercises you will see something like this

  ++++++++++++++++++++++++++++++++++++++++++++++++++
  Error check
  --------------------------------------------------
  --------------------------------------------------

• This is the test script running your code looking for Unix errors
• If you see nothing between the two lines of dashes, ----, your script is good
• If the output of your script is missing something or produces incorrect output ...
• you will hear a beep ...
• and see an error message

Getting Help

• This course makes you do things that you may not have done before
• Whenever you do something new there is always a good chance you will make a mistake
• When this happens, the first thing you should do is reread the instructions
• Mistakes often happen when we read too fast
• If you cannot fix the problem in a reasonable amount of time, ask for help
• There are two ways you can do this
  • Post a question in the class discussion area
  • Email the Class Assistant
• DO NOT EMAIL ME with your question
• I have over 100 student each semester
• With that workload I must be very careful how I spend my time
• I would rather respond to your question on Piazza than in an email
• Only one student will see an email response
• But an answer on Piazza can be seen by the entire class
• Only send me an email when you have an issue that affects you and you alone
• Like being out of the country due to a family emergency

Describing a Problem

• You can't get help with a problem unless you describe it well
• Statements like the following are useless when asking for help
  • It does not work
  • I get an error when I run the code
• You have to describe the specific circumstances that caused the problem
• The best way to do this is with the actual text from the ssh client window
• Copy both what you typed, and what happened after you hit Enter
• Something like this

  it244gh@itserver6:~/it244/ex$ mkdr ex2
  No command 'mkdr' found, did you mean:
   Command 'mkdir' from package 'coreutils' (main)
  mkdr: command not found
  it244gh@itserver6:~/it244/ex$

Don't Use Screenshots in Piazza

• Many students paste screenshots of code into Piazza
• This is not a good idea
• I have a hard time reading some of the screen shots
• And I can't copy the code into the Python interpreter to test it
• Instead copy the code to your class directory
• And type the name of your file into your Piazza entry
• This way I can run the code myself
• And use various debugging techniques

Review

Shells

• The shell is the program that gives you the command line
• You use the command line to run programs
• Modern shells provide a number of features that make them easier to use
• Down through the years there have been a number of different Unix shells
• Today, the two most common shells are the TC shell and Bash
• We will be using Bash in this course

Unix Commands

• Unix commands are programs
• To run a Unix command type the program name on the command line
• Sometimes you want that command to work on something like a file or directory
• To do this you type the name of the file or directory after the command
• This is called an argument
• Some commands have options which appear right after the command
• Options change what the command does
• For example the ls command lists the contents of a directory

  $ ls
  foo.txt  it244  work

• When ls is used with the -l (for long) option, you get more information

  $ ls -l
  total 3
  -rw-r--r-- 1 it244gh libuuid  16 2012-06-26 16:19 foo.txt
  lrwxrwxrwx 1 it244gh libuuid  34 2012-02-07 09:46 it244 -> /courses/it244/s19/ghoffman/it244gh
  drwxr-xr-x 2 it244gh libuuid 512 2012-06-27 11:08 work

• If ls is given the name of a directory as an argument it will list the contents of that directory

  $ ls html
  it116_html  it117_html  it244_html

Attendance

New Material

The Command Line

• In this course we will be using the command line
• On the command line, you talk to the machine by typing
• You have to be careful what you type
• If you make a mistake of even one characters the command will not work
• This is not the way most of you have interacted with computers
• You are used to a Graphical User Inteface
• GUIs use windows, icons, menus and buttons to make it easy to talk to a computer
• The command line is NOT a user friendly environment
• I sometimes call it user hostile
• So why do we study the command line?
• Because the command line has more power
• Programs written with a GUI take time to create and maintain
• They will never have all the features of the command line
• Most Linux/Unix server installations never install a GUI
• A GUI uses system resources that are better spent on services
• The commands you type at the command line can be put into text files
• These files are called shell scripts
• Instead of typing the commands, you can simply run the shell script
• This makes it easy to automate routine tasks

The Unix script Command

• Sometimes it is useful to keep a record of your Unix session
• For example, when you are running software to install a package
• When you run an installer you usually answer a number of questions
• It's good to have a record of your answers if you run into trouble later
• Unix provides the script command to keep a record of a shell session
• When you run script, Unix creates a new shell session
• Then everything that appears on the screen is stored in a text file
• Everything you type ...
• and everything that is printed in reply
• If you run script with no argument, the name of the text file will be typescript
• This file will be created in the directory you were in when you ran script
• To end the script session, type exit at the command line
• script does not save anything to disk until you type exit
• If you want to add to the bottom of an existing typescript file run

  script -a 

• If you don't you will lose what was in the original file
• It will be overwritten with the text from the new session
• When you end a script session you will be back in the original directory
• This will happen even if you changed directories in your script session

The Editor Used in This Class

• Unix can be customized in many ways
• All these customizations are done by editing text files
• This means you need to know how to use a Unix text editor
• A text editor creates a file that only contains characters
• It does not contain formatting information like bold or italic
• Most Unix system administrators use the vim text editor
• vim is an updated version of the vi editor
• The textbook devotes an entire chapter to vim and another chapter to emacs
• emacs is preferred by programmers
• I don't want to spend class time teaching you either editor
• The only way to learn an editor is to use it
• Both vim and emacs have many features
• So using them can be very confusing at first
• Today I'll show you nano, a simple text editor
• Today's Class Exercise will give you some practice with nano
• You are free you use any Unix text editor in this class
• Do not use a word processor, such as Microsoft Word
• These programs create files with non-printing format characters
• Such files are useless on Unix
• If you submit work NOT not created by a text Unix text editor you will lose points

The nano Text Editor

• nano is a simple text editor created as part of the GNU project
• In nano you issue a command by holding down the Control key while pressing a letter
• You can move to the beginning of a line of text by pressing Control A
• Control E will move the text insertion point to the end of the line
• The Control key is a modifier key like the Shift key
• You hold down the Shift key to capitalize a letter
• You hold Control key while pressing a letter to make something happen
• When I write "Control A" it does not mean hold down the Shift key along with the Control key
• I mean hold down the Control key while pressing the A key
• Some of the basic nano commands appear at the bottom of the page
• The ^ in this list of commands stands for the Control key
• So ^O means Control O
• The nano feature set is limited
• You can only work with one file at a time
• You can search for text but there is no search and replace feature
• nano does have a limited cut and paste feature
• If you press Control K the entire line will disappear
• You can then go to another line and hit Control U
• The line will be pasted back at that point
• When you want to save a file you hit Control O
• The name of the file will appear at the bottom of the screen
• You need to hit Enter to accept that name and complete the save process
• Control X will quit nano
• I have created a web page with instructions for using nano here
• There is a link to it on the class web page

Retrieving Your Last Command

• What do you do when the command does not work?
• You need to run it again, fixing your mistake
• But if you try to type in the command all over again you could make a different mistake
• Fortunately, Bash can help
• Bash remembers your previous command lines and lets you run them again
• This feature allows you to retrieve the last command you typed
• You use this feature by pressing the Up and Down arrow keys
• To retrieve the last command, simply hit the Up arrow
• To retrieve the next to last command, hit the Up arrow twice
• You can use the Down arrow to go in the opposite direction
• Get in the habit of using this history feature
• It can save you a lot of typing

Correcting Mistakes on the Command Line

• The command line is not a user friendly environment
• There are no menus
• You have to remember the names of all commands
• This is one reason Unix command names tend to be short
• If you misspell a command, Unix responds with a cryptic error message
• Fortunately, Unix provides command line editing
• This means you can change what appears on the command line before you run it
• Control A moves to the beginning of the command line
• Control E moves to the end of the command line
• Control U removes all text from your current position to the beginning of the line
• Control K removes all text from your current position to the end of the line
• Any text deleted by using Control U or Control K is stored in memory
• You can paste it back on the command line using Control Y
• The Right and Left arrow keys move the text insertion point back and forth
• Today's class exercise will let you practice these features

Stopping a Running Program

• Most commands run quickly
• But some programs, like a compiler, can take a long time to finish
• Every once in a while you run a command that never seems to finish
• When you need to abort a running program use Control C
• This will work on most Unix systems

Using Options with Unix Commands

• Most Unix commands have options which modify their behavior
• These options appear after the command
• You must type a space before entering the option
• Before the GNU project, most options used a single letter and were preceded by a single dash
• Most GNU utilities use options which consist of words preceded by two dashes
• Often, commands will support both option formats

  $ cat --help
  Usage: cat [OPTION]... [FILE]...
  Concatenate FILE(s), or standard input, to standard output.
  
  -A, --show-all           equivalent to -vET
  -b, --number-nonblank    number nonempty output lines
  ...

Getting Help with Unix Commands

• Most Unix commands have a help option, --help
• This option will provide a brief description of the command
• It will also provide a list of options

  $ ls --help
  Usage: ls [OPTION]... [FILE]...
  List information about the FILEs (the current directory by default).
  Sort entries alphabetically if none of -cftuvSUX nor --sort.
  
  Mandatory arguments to long options are mandatory for short options too.
    -a, --all                  do not ignore entries starting with .
    -A, --almost-all           do not list implied . and ..
    ...

The System Manual

• Unix comes with two extensive documentation systems
• The first system consist of the man pages
• To use this system type man followed by the name of the Unix command

  $ man ls

• The man pages are usually several screens in length
• Hit the Enter key to move down one line
• Or hit the Space bar to move to the next screen
• To exit, type q
• You can move up and down through the man pages using the Up and Down arrow keys
• The man pages are often very technical
• They can be quite intimidating
• But you don't have to read all of the page
• You only have to read enough to answer your question
• I usually read the first few lines which show the arguments expected
• Then I skim down the list of options
• Learn the art of reading just enough to get the job done
• A dear friend of mine called this "guerrilla reading"
• Go in
• Get what you need
• And get out

The info System

• Linux also provides an entirely different documentation system
• This system is menu-based and was created by the GNU project
• To enter this system use the info command
• You can follow info with the name of a command
• If you don't give an argument to info you will see an introductory section
• The Up and Down arrow keys will move up and down one line at a time
• The Space bar moves you down one screenful
• The info system uses links which are indicated by an asterisk, *
• To use a link, move down to a line with an asterisk and hit Enter
• This will take you to a new page
• To return to where you were, type l (the letter "el") for "last"
• Type h for help
• When you are done with the help page type l (el)
• To leave the info system type q
• info is better than man for commands created by the GNU project

Searching for a Keyword with apropos

• man pages are useful but you know the name of the command
• What if you know there is a command but you don't know its name?
• apropos was created to help with this problem
• Follow apropos with a key word and it will give you a list of man page topics

  $ apropos who
  at.allow (5)         - determine who can submit jobs via at or batch
  at.deny (5)          - determine who can submit jobs via at or batch
  bsd-from (1)         - print names of those who have sent mail
  btrfs-filesystem (8) - command group of btrfs that usually work on the whole filesystem
  from (1)             - print names of those who have sent mail
  rwho (1)             - who is logged in on local machines
  rwhod (8)            - system status server
  w (1)                - Show who is logged on and what they are doing.
  w.procps (1)         - Show who is logged on and what they are doing.
  who (1)              - show who is logged on
  whoami (1)           - print effective userid
  whom (1mh)           - report to whom a message would go

Getting Help from the Internet

• The Internet is also a very good source of information about Linux
• If you get a strange error message, try typing it into Google
• There is a large amount of Linux documentation on the web
• One place to start is the Linux Documentation Project which you will find at www.tldp.org

Homework Directories

• When you first log in, you will be in your home directory
• The name of this directory is your Unix account name
• You homework needs to go into another directory
• Each of you should have a class directory, it244, in your home directory
• For each homework assignment you must create a new homework directory inside your hw directory
• The name of this directory must be "hw" followed by the number
• So directory for homework 2 should be hw2
• I use a shell script to collect your homework
• If you put your homework in a different place the script will fail
• Grading homework takes a lot of time
• Having to search for your work makes the grading take longer
• If you put your homework in the wrong directory you will get a 0 for the assignment

Using script in Homework 2

• Homework 2 is your first homework assignment using Unix
• The assignment must be done on pe15.cs.umb.edu
• You need to create a text file using nano or some other Unix text editor
• You will also be asked to run script and do 12 things
• I will look at the typescript file you create to see if you have completed the work correctly
• Your script session does not have to be perfect
• If you make a mistake while running script simply try again
• The best thing to do is to practice the commands before you use script
• When you have a list of commands that work, you can then run them in a script session
• Be sure to check your work

Class Exercise

Class Quiz