3.1 The Source DirectoryIndex

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).

4.1 Set UpIndex

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 IIndex

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 filesIndex

1. Review the Class Notes:
   • Shell Variables - Basics (non-scripting)
   • Login and Shell Startup Files, aliases, options: .bash_profile and .bashrc

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 IIIndex

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):

0. 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

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

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

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

4. 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 doneIndex

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)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.