Updated: 2013-10-26 04:54 EDT

1 Due Date and DeliverablesIndexup to index

WARNING: Some inattentive students upload Assignment #6 into the Assignment #5 upload area. Don’t make that mistake! Be exact.

2 Purpose of this AssignmentIndexup to index

This assignment is based on your weekly Class Notes.

  1. Practice Quoting strings as command line arguments.
  2. Create your Startup Files profile files with sysadmin aliases and options.

Remember to READ ALL THE WORDS to work effectively and not waste time.

3 Introduction and OverviewIndexup to index

This is an overview of how you are expected to complete this assignment. Read all the words before you start working.

  1. Complete the Tasks listed below.
  2. Verify your own work before running the Checking Program.
  3. Run the Checking Program to help you find errors.
  4. Submit the output of the Checking Program to Blackboard before the due date.
  5. READ ALL THE WORDS to work effectively and not waste time.

You will create file system structure in your CLS home directory containing various directories and files. You can use the Checking Program to check your work as you do the tasks. You can check your work with the checking program as often as you like before you submit your final mark. Some task sections below require you to finish the whole section before running the checking program; you may not always be able to run the checking program successfully after every single task step.

When you are finished the tasks, leave these files, directories, and links in place on the CLS as part of your deliverables. Do not delete any assignment work from the CLS until after the term is over!

Edit a file to fix the Quoting to protect all shell meta-characters.

Use a text editor to create your Startup Files login profile files .bashrc and .bash_profile.

Assignments may be re-marked at any time on the CLS; you must have your term work available on the CLS right until term end.

Since I also do manual marking of student assignments, your final mark may not be the same as the mark submitted using the current version of the Checking Program. I do not guarantee that any version of the Checking Program will find all the errors in your work. Complete your assignments according to the specifications, not according to the incomplete set of the mistakes detected by the Checking Program.

3.1 The Source DirectoryIndexup to index

All references to the “Source Directory” below are to the CLS directory ~idallen/cst8207/13f/assignment06/ and that name starts with a tilde character ~ followed by a userid with no intervening slash. The leading tilde indicates to the shell that the pathname starts with the HOME directory of the account idallen (seven letters).

4 TasksIndexup to index

4.1 Set UpIndexup to index

  1. Create the following directory structure in your CLS HOME directory and record (for study purposes) the series of Unix commands you used to create it. Spelling and capitalization must be exactly as shown:

    CST8207-13F
    `-- Assignments
        `-- assignment06

    This directory is the base directory for most pathnames in this assignment. Store your scripts and answers here.

Run the Checking Program to verify your work so far.

4.2 Part A - Quoting exercise IIndexup to index

  1. Make the above assignment06 directory your current directory and copy the script file test.sh from the Source Directory into your own file test.sh (and remember to always use the file copy option that preserves file attributes such as timestamps).

  2. Execute this file (enable execute permissions and then run it) or use bash to read the file so that all the commands inside it execute:

    $ chmod ugo+x test.sh
    $ ./test.sh
    ** - OR USE BASH: - **
    $ bash ./test.sh
  3. Note that the output doesn’t match what is written in the script file. (For example: the quotes are missing, GLOB characters and variables are expanding, and the spacing of the words is different.)

    Fix the Quoting inside the file so that every line is fully quoted to appear exactly as written, blanks included, with no meta-character expansion by the shell. The correct output should give eight lines and look exactly like this when you are finished (including all the extra spaces between some of the words):

    Where is the question mark after the file /etc/passwd?
    Is one also missing after /etc/group?
    The shell prompt is contained in the  $PS1  variable.
    This isn't appearing on my screen properly.  It's missing some quotes.
    This is also "missing" some quotes.  It is not "right" yet.
    This is also "missing" quotes.  It's output that doesn't make sense.
    This isn't working either.  The shell gives an error message.
    ***  This is a file to practice shell quoting.  ***

    You must edit the file to make the entire line of text on each line one argument to echo. You can check your success by temporarily substituting the argv.sh program from the Class Notes for the echo command. (You have to put the argv.sh program into the same directory as test.sh under the name argv.sh and make it executable. Read the test.sh file for details on using an alias in this file to run this program. Remember to return the script to using only echo after your testing.)

    You’ll know you got it mostly right when you see this wc and sum output (but you’ll need to verify one-argument-per-echo using the argv.sh program):

    $ ./test.sh | wc
    8 77 461
    $ ./test.sh | sum
    39169   1

    If your word count is correct but the number of characters is less, you probably failed to make the entire text one argument to echo on each line. You must use Quoting to hide all the blanks and special characters from the shell on each of the lines. The argv.sh program will tell you if you got it right.

  4. When the edited script output is correct, run the script and redirect the script output into file testout.txt

Run the Checking Program to verify your work so far.

4.3 Part B - Creating profile filesIndexup to index

  1. Review the Class Notes:
  2. Use a text editor to create your .bash_profile and .bashrc files with some or all of the suggested content described in the page Startup Files.

    Read the man pages for each command to know what the options to each command mean. The cp -p option is very useful for sysadmin.

    Do not set any options or aliases in your .bashrc that you do not understand! If you don’t know the meaning of a setting, don’t use it. You can RTFM in the bash man page for all BASH settings, and RTFM in command man pages to learn about options to commands.

    I will be spot-checking your knowledge of your aliases. Students using aliases they don’t understand will experience much confusion trying to do future assignments. Only use aliases you understand.

  3. Using the PS1 variable from Worksheet #2 HTML, set your prompt to include your user name, your computer name, and the basename of your current working directory. Put this setting at the bottom of your .bashrc file.

  4. Verify that nothing prints on your screen after you enter your password when you run the non-interactive shell connection using ssh localhost true (as described in the section on Non-interactive shells and PS1:

    $ ssh localhost true
    *** COURSE LINUX SERVER ***
    user@localhost's password:
    $

    For non-interactive commands to work properly, there must be no output on your screen after you enter your password using the above non-interactive command line using the true command.

Your instructor will mark the .bashrc and .bash_profile files in your account on the assignment due date. Do not upload them to Blackboard. Leave them there on the CLS. Do not delete anything.

Run the Checking Program to verify your work so far.

4.4 Part C - Quoting exercise IIIndexup to index

On the CLS run an SSH remote shell command to localhost to verify that it works:

$ ssh localhost "date ; whoami ; echo Hello World"
*** COURSE LINUX SERVER ***
abcd0001@localhost's password:
Thu Oct 17 21:11:44 EDT 2013
abcd0001
Hello World

Above, we use quotes to hide the semicolons from the local shell so that they get passed to the remote shell, when they are again treated as metacharacters and allow multiple commands to be written on one line. The remote shell executes three commands and sends the three outputs back to our screen.

Two shells are involved; one on the local machine to prepare the command line, and another on the remote machine to execute it.

The act of using SSH to send a command to a remote machine strips two levels of quoting from the line being sent. You can see this by putting an echo in front of the command, to see what is actually being sent to the remote system’s shell:

$ echo ssh localhost "date ; whoami ; echo Hello World"
ssh localhost date ; whoami ; echo Hello World

The above echo output shows that the shell running on the remote machine will get the line without any quotes around it, and so the remote shell will expand all the metacharacters and execute three commands.

To quote something on the remote machine in the remote shell requires careful thought. One level of quotes isn’t enough. You need one level of quotes for the shell you’re typing into on the local machine, and another level of quotes that get sent to the remote shell:

$ echo "echo Hello         World"             # only one level of quotes
echo Hello         World                      # note lack of quotes
$ ssh localhost "echo Hello         World"
Hello World                                   # no quotes; blanks disappear

$ echo "echo 'Hello         World'"           # two levels of quotes
echo 'Hello         World'                    # now it has quotes
$ ssh localhost "echo 'Hello         World'"
Hello         World                           # quoted blanks are preserved

Sending the line to a remote login shell works similarly to echoing the command line from the current shell into another local bash shell through a pipe (except in the above case, the bash shell is on a remote machine). Locally, it looks like this, and again two shells are involved and two levels of quotes are stripped:

$ echo "date ; whoami ; echo Hello World"
date ; whoami ; echo Hello World
$ echo "date ; whoami ; echo Hello World" | bash
Thu Oct 17 21:12:44 EDT 2013
abcd0001
Hello World

You can also see this two-level quote stripping by echoing a doubly-quoted string from the current shell into a second local shell:

$ echo "echo Hello         World"             # only one level of quotes
echo Hello         World                      # note lack of quotes
$ echo "echo Hello         World" | bash      # two levels of shell
Hello World                                   # no quotes; blanks disappear

$ echo "echo 'Hello         World'"           # two levels of quotes
echo 'Hello         World'                    # now it has quotes
$ echo "echo 'Hello         World'" | bash    # two levels of shell
Hello         World                           # quoted blanks are preserved

Quotes that you want sent to the remote shell themselves need quoting to protect those quotes from the local shell. One strategy is to single-quote all the double quotes and double-quote all the single quotes:

$ echo echo '"'                               # one level of shell
echo "                                        # note lack of quotes
$ echo echo "'"'"'"'"                         # quote all the quotes
echo '"'                                      # now it has quotes
$ ssh localhost echo "'"'"'"'"                # send to remote shell
"                                             # quoted quote is preserved
$ echo echo "'"'"'"'" | bash                  # or use two levels of shell
"                                             # quoted quote is preserved

Here is your assignment: Instead of having the remote shell echo the words Hello World, have it echo exactly the outputs shown below. Create ssh command lines that follow ssh localhost with a correctly quoted remote shell echo command that will produce each of the shown outputs below exactly, including the extra blanks between the words. The first solution is given to you (several solutions are possible – you only need to find one):

  1. Echo this: Eat ; Pray ; Linux
    Solution: $ ssh localhost echo "'Eat ; Pray ; Linux'"
    Output: Eat ; Pray ; Linux
    Solution: $ ssh localhost echo '"Eat ; Pray ; Linux"'
    Output: Eat ; Pray ; Linux
    Solution: $ ssh localhost echo Eat\\\ \\\ \\\;\\\ \\\ Pray\\\ \\\ \\\;\\\ \\\ Linux
    Output: Eat ; Pray ; Linux

  2. Echo this: Glob /etc/passwd* matches two files.
    Solution 1? $ ssh localhost ...
    Output: Glob /etc/passwd* matches two files.

  3. Echo this: I'm a happy camper.
    Solution 2? $ ssh localhost ...
    Output: I'm a happy camper.

  4. Echo this: One environment variable is $SHELL (the shell)
    Solution 3? $ ssh localhost ...
    Output: One environment variable is $SHELL (the shell)

  5. Echo this: It's evident that "love" > $$
    Solution 4? $ ssh localhost ...
    Output: It's evident that "love" > $$

Each of the above problems has at least three solutions, one using each of the three types of quoting. You only need to find one quoting solution for each question, and your solution might also mix quoting styles.

Use a text editor to put each of your four ssh command line solutions into a file of the form quoteN.sh where N is replaced by the question number, e.g. the file quote0.sh would contain the one line:

ssh localhost echo "'Eat  ;  Pray  ;  Linux'"

(Note the extra blanks required between the words! Count your blanks to match the question!) You can test each file by handing the file to the shell for execution, e.g. run sh quote0.sh.

Hints: First make sure you can use echo or argv.sh without SSH to display the line correctly on your screen, then add the extra quoting needed to pass the line and all its quoting to a remote shell via SSH.

While you are testing, you can get the same quoting output results more quickly using the shell keyword eval in place of ssh localhost above:

$ ssh localhost echo Eat\\\ \\\ \\\;\\\ \\\ Pray\\\ \\\ \\\;\\\ \\\ Linux
*** COURSE LINUX SERVER ***
abcd0001@localhost's password:
Eat  ;  Pray  ;  Linux

$ eval echo Eat\\\ \\\ \\\;\\\ \\\ Pray\\\ \\\ \\\;\\\ \\\ Linux
Eat  ;  Pray  ;  Linux

$ eval ./argv.sh Eat\\\ \\\ \\\;\\\ \\\ Pray\\\ \\\ \\\;\\\ \\\ Linux
Argument 0 is [./argv.sh]
Argument 1 is [Eat  ;  Pray  ;  Linux]

You can use argv.sh to verify that the string is one single argument to the remote echo command. Making the output one argument is not a requirement of this assignment, but doing so confirms that you know how to properly escape a remote shell command.

Run the Checking Program to verify your work so far.

4.5 When you are doneIndexup to index

That is all the tasks you need to do.

Check your work a final time using the Checking Program and save the output as described below. Submit your mark following the directions below.

4.6 Part D - CentOS Configured Installation (future)Indexup to index

Carefully and precisely follow the directions to install CentOS 6.4 server edition into a virtual machine on your mobile device. The installation notes give you ways to verify that your configuration is correct. If you have any doubts, contact your instructor. This work will not be checked until your next assignment. Checking the installation is not part of the current assignment.

5 Checking, Marking, and Submitting your WorkIndexup to index

Summary: Do some tasks, then run the checking program to verify your work as you go. You can run the checking program as often as you want. When you have the best mark, upload the marks file to Blackboard.

  1. There is a Checking Program named assignment06check in the Source Directory on the CLS. You can execute this program by typing its (long) pathname into the shell:

    $ ~idallen/cst8207/13f/assignment06/assignment06check

  2. Execute the above “check” program. This program will check your work, assign you a mark, and display the output on your screen. (You may want to paginate the long output so you can read all of it.)

    You may run the “check” program as many times as you wish, to correct mistakes and get the best mark. Some task sections require you to finish the whole section before running the checking program at the end; you may not always be able to run the checking program successfully after every single task step.

  3. When you are done with checking this assignment, and you like what you see on your screen, redirect the output of the Checking Program into the text file assignment06.txt under your assignment06 directory on the CLS. Use the exact name assignment06.txt in your assignment06 directory. Case (upper/lower case letters) matters. Be absolutely accurate, as if your marks depended on it. Do not edit the file. Make sure the file actually contains the output of the checking program!

  4. Transfer the above assignment06.txt file from the CLS to your local computer and verify that the file still contains all the output from the checking program. Do not edit this file! No empty files, please! Edited or damaged files will not be marked. You may want to refer to your File Transfer notes.

  5. Submit the assignment06.txt file under the correct Assignment area on Blackboard (with the exact name) before the due date. Upload the file via the assignment06 “Upload Assignment” facility in Blackboard: click on the underlined assignment06 link in Blackboard. Use “Attach File” and “Submit” to upload your plain text file.

    No word-processor documents. Do not send email. Use only “Attach File”. Do not enter any text into the Submission or Comments boxes on Blackboard; I do not read them. Use only the “Attach File” section followed by the Submit button. (If you want to send me comments about your assignment, use email.)

  6. Your instructor may also mark the assignment06 directory in your CLS account after the due date. Leave everything there on the CLS. Do not delete any assignment work from the CLS until after the term is over!

Use the exact file name given above. Upload only one single file of plain text, not HTML, not MSWord. No fonts, no word-processing. Plain text only.

Did I mention that the format is plain text (suitable for VIM/Nano/Pico/Gedit or Notepad)?

NO EMAIL, WORD PROCESSOR, PDF, RTF, or HTML DOCUMENTS ACCEPTED.

No marks are awarded for submitting under the wrong assignment number or for using the wrong file name. Use the exact name given above.

WARNING: Some inattentive students don’t read all these words. Don’t make that mistake! Be exact.

READ ALL THE WORDS. OH PLEASE, PLEASE, PLEASE READ ALL THE WORDS!

Author: 
| Ian! D. Allen  -  idallen@idallen.ca  -  Ottawa, Ontario, Canada
| Home Page: http://idallen.com/   Contact Improv: http://contactimprov.ca/
| College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/
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