Updated: 2018-10-26 09:25 EDT

1 Due Date and DeliverablesIndexup to index

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 and BackgroundIndexup to index

This assignment is based on your weekly Class Notes and covers these topics:

  1. Create your new 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.

3 How to complete this AssignmentIndexup to index

For full marks, follow these directions exactly:

  1. These tasks must be done in your account via Remote Login to the Course Linux Server.

  2. Do the tasks in order, from top to bottom. Do not skip steps. Most tasks are independent, but some depend on successful completion of a previous task.

  3. READ ALL THE WORDS in each task before you begin the task, especially all the Hints and links.

  4. Verify your own work before running the Checking Program. You won’t have a checking program at your job interview and the Checking Program is not guaranteed to check everything.

  5. Run the Checking Program at the end of the task to grade your work and help you find some of your errors. A perfect mark from the Checking Program does not mean your answers are correct.

  6. When you are done with this Assignment, submit the output of the Checking Program to Brightspace before the due date, following the directions given at the end of this Assignment.

3.1 Notes on doing assignment workIndexup to index

  1. You can use the Checking Program to check your work after you have completed each task.

    Most task sections below require you to finish the whole task section before running the Checking Program. You may not always be able to run the Checking Program successfully in the middle of a task or after every single task sub-step. The assignment tells you where you can safely check your work.

  2. You will create file system structure in your CLS home directory containing various directories and files. When you are finished the tasks, leave the files and directories in place on the CLS as part of your deliverables for your instructor to verify.

    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. Do not delete any assignment work until after the term is over!

  3. You can modify your work and check it with the Checking Program as often as you like before you submit your final mark to Brightspace. You can upload your marks to Brightspace as many times as you like before the due date. Partial marks are accepted.

  4. Your instructor will also mark on the due date the work you do in your account on the CLS. Leave all your work on the CLS and do not modify it after you have submitted your final mark to Brightspace.

  5. 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 future assignments very difficult.

3.2 Searching the course notes on the CLSIndexup to index

All course notes are available on the Internet and also on the CLS. You can learn about how to read and search these CLS files using the command line on the CLS under the heading Copies of the CST8207 course notes near the bottom of the page Course Linux Server. You also learned how to search the notes in Assignment #05 HTML.

3.3 Draw File System DiagramsIndexup to index

Many students find it extremely helpful to draw a quick graph/picture of their file system directory structure on paper before attempting to answer questions about relative pathnames.

You need to be able to visualize the relative locations of names in the file system tree to answer these questions. Draw the trees on paper!

3.4 The Source DirectoryIndexup to index

All references to the Source Directory below are to the CLS directory ~idallen/cst8207/18f/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 TasksIndexup to index

Have you completed all the prerequisites, before attempting these tasks?

4.1 Set Up – The Base Directory on the CLSIndexup to index

  1. Do a Remote Login to the Course Linux Server (CLS) from any existing computer, using the host name appropriate for whether you are on-campus or off-campus. All work in this assignment must be done on the CLS.

  2. Set your PS1 shell prompt, as you did in a previous assignment. This is the last time you will have to do this manually; this assignment configures your .bashrc file.

  3. Create the assignment07 directory in your usual Assignments directory.

    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.

Hints: See your previous assignment for hints on doing the above.

Run the Checking Program to verify your work so far.

4.2 Creating Shell Start-Up FilesIndexup to index

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 shell prompt to include at least the basename of your current working directory. (You may also include things such as your user name and/or your computer name.) Also put this variable setting statement in your .bashrc file.

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

Answers for assignments, tests, and exams expect default shell behaviour with no custom options set. Don’t get confused!

  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 Start-Up Files 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 from your start-up files 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 Brightspace. Leave them there on the CLS. Do not delete anything from the CLS until after the term is over!

Run the Checking Program to verify your work so far.

4.3 Using shell environment variablesIndexup to index

You need to understand Shell Variables to do this task.

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

  1. Make the Base Directory your current directory while you work on this task, so that the file you create is in the current directory. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

envvars.sh

  1. Use the echo command to display on your screen the value of the environment variable containing your HOME directory.

    When you have the right command line, put a copy of the command line into a new file envvars.sh in the Base Directory (which should be your current directory). (Put a copy of the command line in the file, not the command output.) You should use a text editor such as The VI Text Editor to create this new file.

    The file should now contain one command line – exactly the same command line that you typed to display the HOME value above. Look at the contents of the file to make sure it is exactly the same as the command line you used.

    If you run the file you created using the shell, it should print just the value of your HOME directory variable, similar to this:

    $ sh -u envvars.sh
    /home/abcd0001
    
    $ HOME=foobar sh -u envvars.sh
    foobar
  2. Use the echo command to display on your screen the value of the environment variable containing your userid.

    When you have the right command line, append a copy of the command line to the end of the file envvars.sh in the Base Directory. (Append a copy of the command line to the file, not the command output.) You should use a text editor such as The VI Text Editor to edit the file and add the line to the end of this file.

    The file should now contain just two command lines. If you run the file using the shell, it should print the value of your HOME directory variable and then your userid variable, similar to this:

    $ sh -u envvars.sh
    /home/abcd0001
    abcd0001
  3. Use the echo command to display the value of the environment variable containing your assigned shell.

    When you have the right command line, append a copy of the command line to the end of the file envvars.sh in the Base Directory. (Append a copy of the command line to the file, not the command output.) The file will contain three command lines and should output three lines when you use the shell to run it, similar to this:

    $ sh -u envvars.sh
    /home/abcd0001
    abcd0001
    /bin/bash
  4. Use the echo command to display the value of the environment variable containing your shell search path. Add the command you use to do this to the end of file envvars.sh. The file will contain four command lines and should output four lines when run by the shell.

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

  6. To verify that you have used proper procedures for expanding variables inside your script, set the HOME variable to be a GLOB character temporarily and then run the script again like this:

    $ HOME='*' sh -u envvars.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 all the words in the paragraph about double-quoting at the start of this task, above.

  7. Use a text editor such as The VI Text Editor to edit the file and add four or more shell comment lines to the end of the file, naming each environment variable, in order, and describing in your own words the use for or meaning of that variable in your script. The resulting file will be exactly eight lines long: four command lines followed by four comment lines starting with variable names.

    A shell comment line starts with a number sign (octothorpe, pound-sign, or hashtag) character “#” and is no longer than 80 characters, e.g.

    # NAME1 This is a shell comment line.  It starts with the # character.
    # NAME2 Comment lines should be shorter than 80 characters in this course.
    # NAME3 Comment lines should be added to the bottom (end) of the file.
    # NAME4 You need exactly four comment lines in the file, one per variable.
    1. Replace the four NAMEs with the names of each of the four environment variables in the first four lines of the script.
    2. Use your own words (do not copy mine or others) in your comment lines.
    3. Use one comment line for each of the four variables, in order.
    4. The comment lines should all be on new, separate lines; do not add comments to the ends of any executable lines in the file.
    5. Do not put any blank lines in the file (lines with nothing on them). Every line should contain some text. No blank lines. Use a program to count the lines in the file to be sure.
    6. Keep each comment line shorter than 80 characters in this course.

    Your instructor will read and verify your comment lines after the due date.

Run the Checking Program to verify your work so far.

4.4 Working with your search PATHIndexup to index

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

There is a Hints section below that you should read if you have trouble with this task. Always read the task to the end, including all the Hints, before you begin!

  1. Make the Base Directory your current directory while you work on this task, so that the file you create is in the current directory. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

workpath.sh

  1. Use a text editor to create a file named workpath.sh under the Base Directory (which should be your current directory). Put these five command lines into the file:

    1. The first command line in the file must safely echo the current value of your search path environment variable onto your screen, as you did above. (Put the command in the file, not the output.)
    2. The second command line must set the shell search path variable to include the Source Directory for this assignment appended at the (right) end. Append the Source Directory absolute pathname to the right end of the current search path variable.
    3. The third command line must safely echo the new value of the search path environment variable onto your screen again.
    4. The fourth command line must be a command line that shows which shell search path directory contains a command named assignment07check (the basename of the Checking Program). This line contains a command name and one argument that must be assignment07check
    5. The fifth command line must have the shell find and execute a command named assignment07check, which it will do using the modified search path that you set earlier in the script. No slashes should appear in this command name, so that the shell uses your modified search path to find it and run it. (Review how the shell search PATH works.)
  2. After you have created your five-line shell script, enable execute permissions on the script file and then run (execute) it using these two command lines:

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

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

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

    1. The first command line of the script will display the current search path environment variable.
    2. The second command line of the script modifies the search path environment variable and will display no output.
    3. The third command line of the script will display the modified search path environment variable.
    4. The fourth command line will display the absolute path of where the shell finds the assignment07check command name, using its own modified search path set on line two.
    5. The fifth command line should have the shell 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 near the beginning (top) of the file.
  5. The command that tells you which PATH directory contains a command name is documented in shell search PATH and is in your List of Commands You Should Know.
  1. As you did in the previous task, add five or more shell comment lines to the bottom (end) of the file, describing in your own words what each line in 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 (at least five, one per command) to describe the script.

Run the Checking Program to verify your work so far.

4.5 Quoting Exercise – Easy VersionIndexup to index

You must know how to use a text editor and understand how shells use Quoting to do this task. Remember to read the Hints below.

  1. Make the Base Directory your current directory while you work on this task, so that the files you create are in the current directory. (Be lazy: Choose a current directory that makes your pathnames as short as possible!)

quoteFixer.sh

  1. Copy the script file badQuotes.sh from the Source Directory into the current directory using the new name quoteFixer.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 at the bottom, 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 the text given to echo on each line is fully quoted to be one single argument to each echo command, and the text must display on 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 missing question mark, after this file name:  /etc/passwd?
    Is the question mark also missing after this file name:  /etc/group?
    Do you see any of the  *[square]*  *[brackets]*  in this line ????????????
    The BASH shell prompt is contained in this upper-case variable:  $PS1
    This line doesn't appear correctly on the screen.  It's missing the quotes.
    This line is also missing "all" the quotes and is "not right" yet!
    This line is also "missing quotes".  It's output that isn't right yet!
    The $SHELL gives an error message on this line;  it isn't working at all.
    *** This file is to practice your $SHELL quoting.  Do you see the line? ***
    Do   you   see   this   last   line   with  all  the   extra   spaces  ?

    The correct script output, as shown above, is exactly ten lines, 123 words, 723 characters and has a checksum of 52180 1.

Hints:

  1. You must edit the quoteFixer.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 all the shell metacharacters, including spaces.

  2. You can check whether you have successfully created one single argument on each line by using an alias to temporarily substitute 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 comments inside the quoteFixer.sh file for details on using an alias to run argv.sh. You have to put the argv.sh program into the same directory as quoteFixer.sh under the name argv.sh and make it executable. See the comments for details.

  3. If your line and word count is correct but the number of characters is less, you probably failed to hide spaces 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. If your output is mostly correct but you can’t find your mistakes, copy and paste the above correct text into a file named correct on the CLS and verify its word count and checksum. Then run your script and save (redirect) the script output in file out. Then use the diff command to compare the two files. The diff command will show you just the lines where the differences are. In the course notes you can learn about how to use diff.

    $ sum correct                      # verify the checksum
    59121 1 correct
    $ ./quoteFixer.sh >out             # save my script output
    $ diff correct out                 # compare correct output with mine
    [... your output here ...]

quoteFixer.txt

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

    The file must contain exactly the same lines, words, and characters as given above. The checksum of the file must be the same as above.

    Hint: Make sure you spell the extension on the pathname correctly.

Run the Checking Program to verify your work so far.

4.6 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 below and save the standard output of that program into a file as described below. Submit that file (and only that one file) to Brightspace following the directions below.

Your instructor will also mark the Base Directory in your account on the due date. Leave everything there on the CLS. Do not delete anything.

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

Nothing seriously bad will happen if you forget to log out, but you may leave behind an empty, “ghost” login session that may take some days to time out and disappear. Always exit before you close your laptop, PuTTY, or Terminal session.

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

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/cst8207/18f/assignment07/assignment07check

    Note the leading tilde ~ character on the command name. You will learn of ways to make this long line shorter in future assignments.

  2. When you are done, 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 assignment 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/cst8207/18f/assignment07/assignment07check >assignment07.txt
    • Use standard 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; the format is fixed.

    You can view the output file one-page-at-a-time using the less program (use the space bar to page forward and use the letter q to quit):

    $ less assignment07.txt
    • In less use the space bar to page forward and use the letter q to quit).
    • 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.
    • 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 or open and save this file on your local computer! 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 single assignment07.txt file from your local computer to the correct A-07 Assignment #07 area on Brightspace before the due date:
    • See Assignment #01 for details on how to upload files to Brightspace.
    • Only upload the one file that is the standard output of the Checking Program.
    • Make sure the file has the correct assignment07.txt name.
    • Make sure you upload it to the right place, not into Assignment 5 or 6!
  6. 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!

Notes:

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

Author: 
| Ian! D. Allen, BA, MMath  -  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/
| Defend digital freedom:  http://eff.org/  and have fun:  http://fools.ca/

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