COMP-206 Introduction to Software Systems

COMP-206 Introduction to Software Systems, Winter 2020

Mini Assignment 2: Bash Shell Scripting

Due Date Jan 30, 23:55

This is an individual assignment. You need to solve these questions on your own. Use the discus￾sion forum on Piazza if you have any questions. You can also reach out to the course email address,

utilize TA/Instructors office hours as necessary. Late penalty is -5% per day. Even if you are late

only by a few minutes it will be rounded up to a day. Maximum of 2 late days are allowed.

You MUST use mimi.cs.mcgill.ca to create the solution to this assignment. You must not use your

Mac command-line, Windows command-line, nor a Linux distro installed locally on your laptop. You can ssh or

putty from your laptop to mimi.cs.mcgill.ca, or you can go to the third floor of Trottier and use any of those

labs to ssh to mimi to complete this assignment. All of your solutions should be composed of commands that are

executable in mimi.cs.mcgill.ca.

Questions in this exercise requires you to turn in two shell scripts. Instructors/TAs upon their discretion may

ask you to demonstrate/explain your solution. No points are awarded for commands that do not execute at all.

(Commands that execute, but provide incorrect behavior/output will be given partial marks.) All questions are

graded proportionally. This means that if 40% of the question is correct, you will receive 40% of the grade.

Please read through the entire assignment before you start working on it. You can loose up to

3 points for not following the instructions. It also has some helpful suggestions and tips that might

save you some trouble.

Labs A through C will provide some background help for this mini assignment.

Unless otherwise stated, all the names of the scripts that you write, commands, options, input arguments, etc.

are implied to be case-sensitive.

Total Points: 20

Ex. 1 — A basic shell script for searching tar files (8 Points)

In class we explored the tar command that can be used to archive files and entire directory structures. Sometimes

we would want to check the contents of a tar file without extracting it back, such as to check if a particular filename

is present in a given tar file. Programmers often keep such handy set of commands written together in the form of

a shell script that can be used repeatedly.

For this task, you will create a shell script named tarzan.sh which accepts 2 arguments – the name of a file, followed

by a tar file’s name. The tar file name maybe passed on using absolute path or relative path. The objective is to

inform the user if a particular file is present in a tar file or not, without extracting it. The tar command provides

you with an option to list all the contents in the tar file without extracting it. Use the man command to explore the

tar command and find this option.

Below is an example (valid) usage.

$ ./tarzan.sh sort.c /archives/2017/gamingProject.tar

2 Points for writing code with proper (readability) indentation and writing necessary comments (required to un￾derstand the logic, etc.) in the code.

1.Use vi to create your script in mimi.cs.mcgill.ca .

2.Ensure that your script can be executed using bash shell.

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3.(2 Points) If the script is not passed two arguments to it, you must throw an error/usage message, such as the

following example.

$ ./tarzan.sh sort.c

Usage ./tarzan.sh filename tarfile

4.(1 Point) If the tar file cannot be found, the script should throw an error message.

$ ./tarzan.sh sort.c /archives/2017/gamingProject.tar

Error cannot find tar file /archives/2017/gamingProject.tar

5.(1 Point) If the tar file is found, but the filename that is searched is not present in it, the script should display

this fact.

$ ./tarzan.sh sort.c /archives/2017/gamingProject.tar

sort.c does not exist in /archives/2017/gamingProject.tar

6.(2 Points) If the script is able to locate the filename in the tar file, it should display the found message.

$ ./tarzan.sh sort.c /archives/2017/gamingProject.tar

sort.c exists in /archives/2017/gamingProject.tar

Ex. 2 — A bash script for file search and content display (12 Points)

Search is a very essential form of interaction with the contents stored in a file system. In this task, you will write a

bash shell script seeker.sh that will look for file names with a specific string in the file name and optionally display

its contents to the screen.

The usage syntax for the script is as follows.

$ /seeker.sh [-c] [-a] pattern [path]

The options/arguments in square brackets are optional, and their intent is as follows.

-c indicates that the script should display the contents of the file. Otherwise only the absolute path to the file

(including file name) is displayed to the screen.

-a indicates that if there are multiple matching files, the output should include all of them. Otherwise only (any)

one of the file is included in the output.

path is the absolute path to the directory under which the script should look for the files. If this argument is not

passed to the script, it is expected to look for files under the ”current directory”.

pattern is a string that you want the script to look for in the name of a file (NOT contents of the file). For example

if pattern is msg, it should match the file names mymsg.txt, msg.txt, random.msg, lastmsgs.txt, etc.

An example output of this script is as below.

$ /seeker.sh -c -a msg /mydata/scribbles

==== Contents of: /mydata/scribbles/msg2.txt ====

Hi, I am msg2.txt

Not all those who wander are lost.

==== Contents of: /mydata/scribbles/msg.txt ====

Hello there, I am msg.txt

2 Points for writing code with proper (readability) indentation and writing necessary comments (required to un￾derstand the logic, etc.) in the code.

1.Use vi to create your script in mimi.cs.mcgill.ca .

2.Ensure that your script can be executed using bash shell.

3.(2 Points) Ensure that your script is passed proper arguments. pattern is the only mandatory input to the

script. An appropriate error and usage message should be raised if proper arguments are not passed into the

script. See examples below.

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$ ./seeker.sh

Error missing the pattern argument.

Usage ./seeker.sh [-c] [-a] pattern [path]

$ ./seeker.sh -c

Error missing the pattern argument.

Usage ./seeker.sh [-c] [-a] pattern [path]

$ ./seeker.sh -a

Error missing the pattern argument.

Usage ./seeker.sh [-c] [-a] pattern [path]

$ ./seeker.sh -c -a

Error missing the pattern argument.

Usage ./seeker.sh [-c] [-a] pattern [path]

4.(1 Point) If the directory passed as argument to the script does not exist, the script should display this fact.

$ ./seeker.sh msg /nosuchdir

Error /nosuchdir is not a valid directory

$ ./seeker.sh -a msg /nosuchdir

Error /nosuchdir is not a valid directory

5.(1 Point) If script cannot find any files with the specified pattern in its name, it should display this information.

$ ./seeker.sh -a meow /etc/cron.d

Unable to locate any files that has pattern meow in its name in /etc/cron.d.

6.(1 Point) When -a option is not passed, include only (any) one matching file in the output.

$ ./seeker.sh msg /scribbles/messages

/scribbles/messages/msg2.txt

7.(1 Point) When -a option is passed, include all the files that match the pattern

$ ./seeker.sh -a msg /scribbles/messages

/scribbles/messages/msg2.txt

/scribbles/messages/msg.txt

8.(2 Points) When -c option is passed, contents of the files must be displayed

$ ./seeker.sh -c msg /scribbles/messages

==== Contents of: /scribbles/messages/msg2.txt ====

Hi, I am msg2.txt

Not all those who wander are lost.

$ ./seeker.sh -c -a msg /scribbles/messages

==== Contents of: /scribbles/messages/msg2.txt ====

Hi, I am msg2.txt

Not all those who wander are lost.

==== Contents of: /scribbles/messages/msg.txt ====

Hello there, I am msg.txt

9.(2 Points) When path argument to indicate the directory to look for files is not passed, search in the current

directory.

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$ cd /scribbles/messages

$ ./seeker.sh -c -a msg

==== Contents of: /scribbles/messages/msg2.txt ====

Hi, I am msg2.txt

Not all those who wander are lost.

==== Contents of: /scribbles/messages/msg.txt ====

Hello there, I am msg.txt

WHAT TO HAND IN

Turn in the 2 shell scripts tarzan.sh and seeker.sh, named properly (so that the TA can identify which script is

for which question. You do not have to zip all of the scripts together.

MISC. INFORMATION

There is a tester script mini2tester.sh that is provided with the assignment that you can use to test how your

scripts are behaving. TAs will be using the exact same tester script to grade your assignment.

$ ./mini2tester.sh

However, it is recommended that when you start writing your scripts, test it yourself first with each option and

arguments such as the ones given in the above examples. Once you are fairly confident that your script is working,

you can test it using the tester script.

You can compare the output produced by running the mini tester on your scripts to that produced by the mini

tester on the solution scripts which is given in mini2tester.out.txt. Other than the names of directories used by

the tester scripts, the remaining contents should match.

FOOD FOR THOUGHT!

The following discussion is meant to encourage you to search independently for creative and optimal ways to perform

rudimentary tasks with less effort and does not impact the points that you can achieve in the above questions.

• Will your script work for both

$ ./seeker.sh -c -a msg

and

$ ./seeker.sh -a -c msg

If not, can you think of a way to address it? Is your approach scalable and easy to maintain if we have three

different options to pass? Does shell provide other efficient mechanisms to read options passed to a script?