Updated: 2015-10-18 22:57 EDT

1 Due Date and Deliverables

Do not print this assignment on paper!

WARNING: Some inattentive students upload Assignment #7 into the Assignment #6 upload area. Don’t make that mistake! Be exact.

2 Purpose of this Assignment

Do not print this assignment on paper! On paper, you cannot follow any of the hyperlink URLs that lead you to hints and course notes relevant to answering a question.

This assignment is based on your weekly Class Notes.

  1. Create your shell start-up files: .bash_profile and .bashrc
  2. Know the values of key shell environment variables.
  3. Work with your shell search $PATH.
  4. Study shell quoting and fix the quoting in a broken shell script.
  5. Create hard links and soft (symbolic) links.
  6. Examine how hard links work with disk usage.

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

3 Introduction and Overview

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

For full marks, follow these directions exactly.

  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 the files and directories in place on the CLS as part of your deliverables. Do not delete any assignment work until after the term is over!

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 Directory

All references to the Source Directory below are to the CLS directory ~idallen/cst8207/15w/assignment07/ and that name starts with a tilde character ~ followed by a user name 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).

You do not have permission to list the names of all the files in the Source Directory, but you can access any files whose names you already know.

4 Tasks

4.1 Set Up – The Base Directory on the CLS

You must keep a list of command names used each week and write down what each command does, as described in the List of Commands You Should Know. Without that list to remind you what command names to use, you will find assignments very difficult.

  1. Do a Remote Login to the Course Linux Server (CLS). All work in this assignment must be done on the CLS.

  2. Set your PS1 shell prompt.

  3. Create the following directory structure in your CLS personal HOME directory and record (for study purposes) the series of Unix commands you used to create it. (You do not have to create any directories that you have already created in a previous assignment.) Spelling and capitalization must be exactly as shown:
    1. Create the CST8207-15W directory in your CLS HOME directory.
    2. Create the Assignments directory in the CST8207-15W directory.
    3. Create the assignment07 directory in the Assignments directory.

Hint: You can create the entire directory tree above using one single command.

This assignment07 directory is called the Base Directory for most pathnames in this assignment. Store your files and answers in this Base Directory, not in your HOME directory or anywhere else.

Run the Checking Program to verify your work so far.

4.2 Creating Shell Start-Up Files

You need to understand Start-Up Files and how to use a text editor such as The VI Text Editor to do this task.

.bash_profile

.bashrc

  1. Use a Linux text editor to create your .bash_profile and .bashrc files with the minimum suggested content described in Start-Up Files. These files do not exist yet; you must create them.

    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.

    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 (or one like it) in your .bashrc file.

    Your .bash_profile must contain only one line. Your .bashrc must contain at least two lines (not including comment lines).

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

  1. 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 after 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.

4.3 Using shell environment variables

Follow correct double-quoting procedures when expanding variables, as noted in Shell Variables.

You may find it convenient to make the Base Directory your current directory while you work on this task. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

You may use a text editor such as The VI Text Editor to create this file.

enviro.sh

  1. Use the echo command to display the value of the environment variable containing your userid. Put the command you use to do this into file enviro.sh in the Base Directory. (Put in the command, not the output.) The file will contain one command line.

  2. Use the echo command to display the value of the environment variable containing your home directory. Append the command you use to do this to file enviro.sh in the Base Directory. (Put in the command, not the output.) The file will contain two command lines.

  3. Use the echo command to display the value of the environment variable containing your assigned shell. Append the command you use to do this to file enviro.sh in the Base Directory. (Put in the command, not the output.) The file will contain three command lines.

  4. Use the echo command to display the value of the environment variable containing your shell search path. Append the command you use to do this to file enviro.sh in the Base Directory. (Put in the command, not the output.) The file will contain four command lines.

  5. Assuming that enviro.sh is in your current directory, use the sh shell to run (execute) your script by typing sh -u enviro.sh and the values of all four environment variables should display on your screen. (If enviro.sh is in some other directory, use the appropriate pathname to it.)

  6. To verify that you have used proper procedures for expanding variables inside your script, set the USER variable to be a GLOB character temporarily and then run the script again like this (assuming that enviro.sh is in your current directory):

    $ USER='*' sh -u enviro.sh

    Make sure that the first line of script output is the single GLOB character * and not a list of file names. If you see a list of file names, re-read the first sentence of this task, above.

  7. Add one or more shell comment lines to the end of the file, describing in your own words the use for or meaning of each of the four variables in your script. A shell comment line starts with a number sign (octothorpe, pound-sign, or hashtag) character #, e.g.

    echo "Hi there."
    # This is a shell comment line.  The shell will ignore it.
    # This is another comment line.  It starts with the # character.
    1. Use your own words (do not copy mine or others) in your comment lines.
    2. Use as many comment lines as you need to describe all four variables.
    3. The comment lines should all be on separate lines; do not add comments to the ends of any executable lines in the file.
    4. Do not put any blank lines in the file. No blank lines.

Run the Checking Program to verify your work so far.

4.4 Working with your search PATH

You must know how to use a text editor and understand how a shell uses a search PATH to do this task.

You may find it convenient to make the Base Directory your current directory while you work on this task. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

pathcheck.sh

  1. Use a text editor to create a file named pathcheck.sh under the Base Directory. This file will contain these four command lines:

    1. The first line must set the shell search PATH variable to include the Source Directory for this assignment appended at the (right) end of the path. Append to the existing PATH variable, as shown in the course notes.
    2. The second line must safely echo the new value of PATH onto your screen. Follow correct double-quoting procedures when expanding variables, as noted in Shell Variables.
    3. The third line must be the command that shows the host name (computer name) of the CLS machine (the same name as seen in the shell prompt).
    4. The fourth line must have the shell find and execute a command named assignment07check (the basename of the Checking Program), which it will do using the modified PATH you set at the top of the script. No slashes should appear in this command name, so that the shell uses your modified $PATH, set on the first line, to find it and run it. (Review how the shell search PATH works.)
  2. After you have created your four-line shell script, enable execute permissions on the script file and then run (execute) it using these two command lines:

    $ chmod u+x pathcheck.sh                       # all lower-case letters
    $ ./pathcheck.sh

    Remember how to make a file executable and run it from the current directory; you will need this again.

    When you run the script, each of the four command lines in the script will execute, one after the other. The first line, setting the search path, should produce no output. There will be three outputs that come from the next three lines of the script:

    1. The second line of the script will display the modified PATH.
    2. The third line will display the name of the machine.
    3. The fourth line should find and run the assignment07check checking program and generate lots of output.

Hints:

  1. You need to know how the shell uses the PATH variable to find and run commands.
  2. You need to know how to append to PATH.
  3. Remember to quote all variable expansions.
  4. If you see command not found output coming from commands inside the executing script, you have either spelled a command name incorrectly or have not correctly set the shell search path inside the script file. This script will only work if the shell search PATH is set correctly at the beginning (top) of the file.
  1. As you did in the previous task, add one or more shell comment lines to the end of the file, describing in your own words what this script does and how it does it. Use your own words (do not copy mine) in your comment lines. Use as many comment lines as you need to describe the script.

Run the Checking Program to verify your work so far.

4.5 Quoting Exercise – Easy Version

You must know how to use a text editor and understand how shells use Quoting to do this task.

You may find it convenient to make the Base Directory your current directory while you work on this task. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

  1. Make the Base Directory your current directory.

goodquotes.sh

  1. Copy the script file badquotes.sh from the Source Directory into the current directory using the new name goodquotes.sh as you copy it.

  2. Enable execute permissions on the script file and run the script (as you did in the previous task).

    Note that the output of running the script generates an error message and the lines output on the screen don’t match what is written in the script file. For example: many quotes are missing, GLOB characters and variables are expanding, and the spacing of the words is different.

  3. Use a text editor to add Quoting inside the script file so that every line is fully quoted to appear onto your screen exactly as written in the file, blanks included, with no meta-character expansion by the shell. The correct ten lines of output should 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?
    Do you see any *[square]* *[brackets]* in this line ?????
    The BASH shell prompt is contained in the  $PS1  variable.
    This isn't appearing on my screen correctly.  It's missing the quotes.
    This is also "missing" all the quotes.  It is "not right" yet.
    This is also missing "quotes".  It's output that doesn't make sense.
    This line isn't working either.  The shell gives an error message.
    ***  This is a file to practice shell quoting.  Do you see this line?  ***
    Do   you   see   this   last   line   with   the   extra   spaces  ?

    The correct script output (above) is exactly ten lines, 106 words, 624 characters and has a checksum of 61815 1.

Hints:

  1. You must edit the goodquotes.sh file to make the entire line of text on each line one single shell argument to echo. Review how the shell finds arguments and how to use Quoting to hide shell metacharacters.

  2. You can check whether you have successfully created one single argument on each line by temporarily substituting the argv.sh program from the Class Notes for the echo command.

    You can easily get a copy of the argv.sh program from the course notes on the CLS using the newnotes symbolic link you created in a previous assignment.

    Read the goodquotes.sh file for details on using an alias inside the quotes file to run argv.sh. You have to put the argv.sh program into the same directory as goodquotes.sh under the name argv.sh and make it executable. Remember to undo the alias and return the script to using only echo after you finish your testing.

  3. If your line and 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.

goodquotesout.txt

  1. When the output of your edited script is correct, run the script and redirect the script output into file goodquotesout.txt in your Base Directory (which should still be your current directory).

    The file must contain exactly ten lines, 106 words, 624 characters and have a checksum of 61815 1.

Run the Checking Program to verify your work so far.

4.7 Hard and Soft Linking exercise

You need to understand Hard Links and Symbolic Links and to do this task.

ln/abcd0001.txt

  1. In your Base Directory, create a sub-directory and an empty file ln/abcd0001.txt (no spaces), where the text abcd0001 is replaced by your own eight-character userid in the file name. NOTE: The sub-directory name is ln (two letters), not 1n (digit letter).

  2. For every unique character in your own eight-character userid, create a sub-sub-directory under ln with that single-character name.

    For example, the userid abca0151 would result in six unique sub-sub-directory names under the ln directory – one sub-sub-directory for each of the unique characters a, b, c, 0, 1, 5. (You can create multiple directories with one single command line.)

    Do this for your own userid, which means you may have more or fewer sub-sub-directories, depending on the letters and digits in your own userid.

  3. Inside each of those new sub-sub-directories, create a single Hard Link to the empty file from the first step. Keep the same file name as the original for each hard link you create. Use hard links, not symbolic links.

    Continuing the above example, the abca0151 user would hard link the original empty file name abca0151.txt into each of those six new sub-sub-directories, creating six additional names for the same file. Keep the same file name as the original for each hard link.

    Check the link counts on everything to make sure that you have created links to the same file and not made copies of the file. Use hard links, not symbolic links.

  4. For every lower-case letter directory name you created, create a short, relative Symbolic Link that is its upper-case equivalent. If you created directory a, then create symlink A that points to a so that both ls ln/a and ls ln/A give identical results. (You must use symbolic links, because you cannot make hard links to directories.)

  5. In every file you have just created in this section, enter the following information, one name per line: Enter the names of the three common file system commands that are “directory only” commands that require permission only on the directory inode to work properly, and that do not require permissions on the file inode to work. The answer is three lines, one command name per line. (See your in-class notes for the three names I wrote on the board, or read the course notes about links and inodes.) The right answer has this format (three lines; three words; nine characters):

    $ wc abcd0001.txt
    3 3 9 abcd0001.txt

    Again, the text abcd0001 must be your own userid, in all cases.

Hints: All the file names you created in this section should be hard links to the same file; you have very little editing to do. The three command names are all commands that are directory operations that manipulate file names; they don’t touch the file data and don’t need any permissions on the file data.

Use your symbolic link ./check (created in the previous task) to run Checking Program to verify your work so far.

4.8 Four Disk Usage Exercises: easy, medium, hard, ug1y

You need to understand Hard Links and Disk Usage to do this task.

Read this task all the way through, especially the Hints, before you delete anything, or else you will have to start over again.

For the next task, you will need to look up the copy option that means archive that preserves hard links (as well as all the other attributes) when you copy a directory (RTFM).

My DiskUse

  1. After you have run the Checking Program at least once, you will find created for you in the Source Directory a disk usage directory named DiskUse/abcd0001 (where abcd0001 is replaced by your own userid). Copy, using the archive option, this directory into your Base Directory using the name My DiskUse. You will know you got it right if your personal copy of the My DiskUse directory has the same disk use summary (du -s) as the one in the Source Directory.

In your personal My DiskUse directory, some of the files are hard links to each other. (If there are no hard links anywhere, you didn’t use the archive option to the copy command that preserves hard links. Delete everything and re-copy.)

Your personal copy of the My DiskUse directory contains exactly four sub-directories, each of which contains many other files and sub-sub-directories. (If you don’t see four sub-directories under your copy of My DiskUse, read all the words in the Hints again.) A recursive list of pathnames under My DiskUse counts 302.

There are four levels of difficulty in this task, one for each of the four sub-directories in your personal My DiskUse directory. Do the easy level first, followed by the medium level, followed by the hard level, followed by the ug1y level.

Read this task all the way through, especially the Hints, before you delete anything, or else you will have to start over again.

4.8.1 The easy level and the three steps A B C

Locate the sub-directory of your personal My DiskUse directory that contains the text easy in the name. Make this your current directory and then follow steps A through C below:

  1. Under the current directory, there is a directory named foo.

  2. Reclaim all the disk space used by the files under foo by removing all the files under foo and any hard links to those files. Some of those hard links may be to files in other sub-directories under the current directory; you don’t have to scan the whole file system to find the hard links. Read the Hints carefully before you remove anything.

  3. Run the Checking Program to verify your work so far. See the Hints if you need to start over.

4.8.2 The medium level

Locate the sub-directory of your personal My DiskUse directory that contains the text medium in the name. Make this your current directory. Repeat the steps A through C above.

4.8.3 The hard level

Locate the sub-directory of your personal My DiskUse directory that contains the text hard in the name. Make this your current directory. Repeat the steps A through C above.

4.8.4 The ug1y level

Locate the sub-directory of your personal My DiskUse directory that contains the text ug1y in the name. (Note carefully the strange spelling, which is not the same as ugly.) Make this your current directory. Repeat the steps A through C above.

4.8.5 Hints for each level: easy, medium, hard, ug1y

Hints: The current directory must be set as given above for each level.

  1. Many of the files in the foo subdirectory in a level have more than one name. Some of those other names may be located in other subdirectories somewhere under the current level. (You don’t have to search the whole disk partition to find them.) The disk blocks for these files in foo will not be freed until you find and remove all their names. Do not remove any names from foo until you also know how to find and remove all the other names for these files. You will need to look at inode numbers to know which files in directory foo are also named in the other directories. You read about how to do this in Disk Usage.

  2. Options to ls to display hidden names and nongraphic (unprintable) characters will be needed for the harder sections. Many names will need to be quoted to hide shell metacharacters (see Quoting).

  3. If you don’t get the right answer for a difficulty level, you can start over by re-copying all or part of your My DiskUse directory from where you originally got it in the Source Directory.

    If you make errors in this task and need to redo one of the four sections, you can remove and re-copy from the Source Directory just the sub-directory for that section. You don’t have to remove and re-copy the whole DiskUse/abcd0001 directory, since that would lose the work you did on the other sections.

    If you do want to remove your entire personal My DiskUse directory to start over, you will need to redo all four levels. If you are smart and rename the directory instead of removing it, you can salvage from the saved directory the parts of the task you have already done successfully, so you won’t have to redo those parts.

  4. If you find that you don’t own any of the files under your My DiskUse directory, and that you have no permission to remove any files, then you didn’t copy the files correctly. Delete everything and re-read and re-do that first step.

4.9 When you are done

That is all the tasks you need to do.

Check your work a final time using the Checking Program below and save the standard output of that program into a file as described below. Submit that file (and only that one file) to Blackboard following the directions below.

When you are done, log out of the CLS before you close your laptop or close the PuTTY window, by using the shell exit command:

$ exit

5 Checking, Marking, and Submitting your Work

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 single file that is the output of the Checking Program to Blackboard.

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.

  1. There is a Checking Program named assignment07check in the Source Directory on the CLS. You can execute this program by typing its (long) pathname into the shell as a command name:

    $ ~idallen/cst8207/15w/assignment07/assignment07check

    You learn one way to make this shorter in the current assignment.

  2. Execute the above Checking Program as a command line on the CLS. This program will check your work, assign you a mark, and display the output on your screen.

    You may run the Checking Program as many times as you wish, allowing you 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 this assignment, and you like the mark displayed on your screen by the Checking Program, you must redirect only the standard output of the Checking Program into the text file assignment07.txt in your Base Directory on the CLS, like this:

    $ ~idallen/cst8207/15w/assignment07/assignment07check >assignment07.txt
    $ cat assignment07.txt
    • Use output redirection with that exact assignment07.txt file name.
    • Use that exact name. Case (upper/lower case letters) matters.
    • Be absolutely accurate, as if your marks depended on it.
    • Do not edit the output file.
    • Make sure the file actually contains the output of the Checking Program!
    • The file should contain, near the bottom, a line starting with: YOUR MARK for
    • Really! MAKE SURE THE FILE HAS YOUR MARKS IN IT!
  4. Transfer the above single file assignment07.txt (containing the output from the Checking Program) from the CLS to your local computer.
    • You may want to refer to the File Transfer page for how to transfer the file.
    • 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. Submit the file exactly as given.
    • The file should contain, near the bottom, a line starting with: YOUR MARK for
    • Really! MAKE SURE THE FILE YOU UPLOAD HAS YOUR MARKS IN IT!
  5. Upload the assignment07.txt file from your local computer to the correct Assignment area on Blackboard (with the exact name) before the due date:
    1. On your local computer use a web browser to log in to Blackboard and go to the Blackboard page for this course.
    2. Go to the Blackboard Assignments area for the course, in the left side-bar menu, and find the current assignment.
    3. Under Assignments, click on the underlined assignment07 link for this assignment.
      1. If this is your first upload, the Upload Assignment page will open directly; skip the next sentence.
      2. If you have already uploaded previously, the Review Submission History page will be open and you must use the Start New button at the bottom of the page to get to the Upload Assignment page.
    4. On the Upload Assignment page, scroll down and beside Attach File use Browse My Computer to find and attach your assignment file from your local computer. Make sure the assignment file has the correct name on your local computer before you attach it.
    5. After you have attached the file on the Upload Assignment page, scroll down to the bottom of the page and use the Submit button to actually upload your attached assignment file to Blackboard.

    Use only Attach File on the Upload Assignment page. Do not enter any text into the Text Submission or Comments boxes on Blackboard; I do not read them. Use only the Attach File section followed by the Submit button. If you need to comment on any assignment submission, send me EMail.

    You can revise and upload the file more than once using the Start New button on the Review Submission History page to open a new Upload Assignment page. I only look at the most recent submission.

    You must upload the file with the correct name from your local computer; you cannot correct the name as you upload it to Blackboard.

  6. Verify that Blackboard has received your submission: After using the Submit button, you will see a page titled Review Submission History that will show all your uploaded submissions for this assignment. Each of your submissions is called an Attempt on this page. A drop-down list of all your attempts is available.
    1. Verify that your latest Attempt has the correct 16-character, lower-case file name under the SUBMISSION heading.
    2. The one file name must be the only thing under the SUBMISSION heading. Only the one file name is allowed.
    3. No COMMENTS heading should be visible on the page. Do not enter any comments when you upload an assignment.
    4. Save a screen capture of the Review Submission History page on your local computer, showing the single uploaded file name listed under SUBMISSION. If you want to claim that you uploaded the file and Blackboard lost it, you will need this screen capture to prove that you actually uploaded the file. (To date, Blackboard has never lost an uploaded file.)

    You will also see the Review Submission History page any time you already have an assignment attempt uploaded and you click on the underlined assignment07 link. You can use the Start New button on this page to re-upload your assignment as many times as you like.

    You cannot delete an assignment attempt, but you can always upload a new version. I only mark the latest version.

  7. Your instructor may also mark files in your 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!

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/
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