Assignment #2 Shell Scripts

COMPSCI 2211b
Software Tools and Systems Programming
Assignment #2
Shell Scripts

Total: 100 Points (5% of Final Grade)
CS2211 - Software Tools and Systems Programming Assignment #2
Learning Outcomes
By completing this assignment, you will gain and demonstrate skills relating to:
ˆ Reading and understanding shell scripts.
ˆ Creating your own shell scripts.
ˆ More practice with tr, grep, wc, sort and head.
Instructions
For this assignment, an electronic submission is required through OWL. This submission should
include a document in PDF format that contains answers for each of the questions listed in the
following sections as well as a copy of each shell script you created in plain text format. Your PDF
file should be named “userid assign2.pdf” where “userid” is your user id. For example, if your
UWO e-mail is “dservos5@uwo.ca” your file should be named “dservos5 assign2.pdf”. Your shell
scripts should be named as per the directions given in the question.
Your answers should be clearly labelled with question and part numbers. Your shell scripts should
be included in both the PDF and as their own plain text file. In addition to your answers, this
document should also contain your full name, student number, UWO user id, the course code, date,
and assignment number.
All Linux commands and shell scripts given must run correctly on the course server
(cs2211b.gaul.csd.uwo.ca) in the Bash shell. A question will only be marked as correct if your
output can be replicated on the course server.
You will be assessed on the following:
ˆ Completion of each question correctly.
ˆ Providing output where required.
ˆ Providing a PDF formatted file following the naming convention.
ˆ Providing a plain text copy of each shell script you create with the correct file name.
ˆ Including your full name, student number, etc. as described above.
ˆ Assignment submission via OWL.
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CS2211 - Software Tools and Systems Programming Assignment #2
Questions
Question 1 (10 Marks)
Consider the following bash script test1:
1 #!/ bin/ bash
2 # My Shell Script !
4 x =$1
5 echo $0
6 echo $1
7 echo $#
8 echo $*
9 echo $x
11 shift
13 echo $0
14 echo $1
15 echo $#
16 echo $*
17 echo $x
(a) Explain what each numbered line of the script does, what it would output (if anything) and
why.
(b) Show the output produced by the following call to test1:
test1 a b c
Question 2 (10 Marks)
Consider the following bash script test2:
1 #!/ bin/ bash
3 echo -n 'Input Number : '
4 read x
6 echo expr $x + 7
7 echo " expr $x + 7 "
8 echo 'expr $x + 7'
9 echo `expr $x + 7`
(a) Explain what each numbered line of the script does, what it would output (if anything) and
why.
(b) Show the output produced by the running test2 and inputting the number 10.
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CS2211 - Software Tools and Systems Programming Assignment #2
Question 3 (15 Marks)
Consider the following bash script good:
1 #!/ bin/ bash
3 echo
4 hour =` date +% H`
6 if [ " $hour " - lt 12 ]
7 then
8 echo " GOOD MORNING "
9 elif [ " $hour " - lt 18 ]
10 then
11 echo " GOOD AFTERNOON "
12 else
13 echo " GOOD EVENING "
14 fi
16 echo
(a) Explain in one or two sentences what this script does.
(b) Rewrite this script to not use elif . Make sure you include a plain text copy of the rewritten
script named good2 in your submission.
Question 4 (20 Marks)
Write a bash shell script called dobackup that does the following in order:
1. Output the text “Input a directory name:”.
2. Read a directory path from the user via standard input. You can assume that the path
contains no spaces and you do not need to support the tilde character (∼).
3. Check if the directory path is valid (i.e. that the directory exists) and print an error and exit
if it is invalid (does not exist).
4. If a directory named backup already exists in the current working directory, delete it and all
the files and subdirectories it contains.
5. Make a copy of the directory given by the user to the current working directory and name it
backup (this copy should contain all files and subdirectories of the original).
6. Use the tar command to make an archive of the backup directory named backup.tar in the
current working directory. We did not go over the tar command in class so it is up to you to
read the man page for tar. You do not need to use compression.
7. Rename backup.tar such that its file name contains the current date in the following format:
backup-<day-<month-<year.tar
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CS2211 - Software Tools and Systems Programming Assignment #2
where <day is the current day (with a leading 0 if one digit), <month is the current month
(with a leading zero if one digit) and <year is the current 4 digit year. For example, if today
was January 31st, 2018 the file should be renamed to backup-31-01-2018.tar
8. Use scp to send a copy of the tar file to a directory in your home directory named mybackups
on the course server (it is assumed that this directory already exists). This command should
be written so it will work on the lab computers or the course server. Rather than using your
username with the scp command use the value of the $USER variable (contains the current
user). It is OK if scp asks the user for their password.
Add comments to your code explaining what every line does as well as a comment at
the beginning of the file (under #!/bin/bash) that contains your name, student number
and a one or two sentence description of what the script does.
Test your script both on the course server and on a lab computer in MC244. Ensure that it works
on both systems and that a copy of your backup archive is sent to the course server in both cases.
Include a plain text copy of your script named dobackup as well as a copy in your PDF file.
Question 5 (20 Marks)
Write a bash shell script called avg that takes the average of the integer arguments given to it on
the command line. The average should be sent to the standard output. Assume that all arguments
are valid integers and that there can be more than 9 arguments.
Your shell script must use a loop and at least one variable.
The number you output should have two decimal places.
Your shell script should output an appropriate error if no arguments are given to it.
You should include a comment at the beginning of the file (under #!/bin/bash) that contains your
name, student number and a one or two sentence description of what the script does. Also add at
least two comments to lines in your script explaining what they do.
Test your script and provide the output for the following commands:
Command Correct Output
avg Need at least one argument!
avg 42 42.00
avg -50 0 50 100 25.00
avg 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 10.50
Make sure to both include your shell script in the PDF and as a plain text file named avg.
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CS2211 - Software Tools and Systems Programming Assignment #2
Question 6 (25 Marks)
Write a bash shell script called nums that takes zero, one or two arguments and gives the following
output:
Command Result (output to standard out)
nums “Usage: nums option filename”
nums 0 “Error: no filename given!”
nums 1 “Error: no filename given!”
nums 2 “Error: no filename given!”
nums 3 “Error: no filename given!”
nums 0 file Outputs the number of lines in the file.
nums 1 file Outputs the file with all letters made upper case and all whole numbers
replaced with *s. For example: “I have 123 apples” would become “I
HAVE * APPLES”.
nums 2 file Outputs only the lines in the file that are 7 letter palindromes.
The palindromes should contain only letters (not numbers or special
characters). The line cannot contain any other text or be any length
other than 7 characters long (not counting line breaks). Capitalization
should be ignored.
nums 3 file Outputs the 4 largest numbers in the file. The file may contain text,
in which case the text should be ignored. Numbers may be on the
same line and separated by spaces or text and/or on different lines.
Hint: You will need to use a combination of the commands cat, head,
tr and sort. Check the man page for sort to learn how to sort numbers
and set the order.
Any other option number “Invalid option!”
If file does not exist “file does not exist!” where file is the name of the file.
You should include a comment at the beginning of the file (under #!/bin/bash) that contains your
name, student number and a one or two sentence description of what the script does. Also add at
least four comments to lines in your script explaining what they do.
Make sure to both include your shell script in the PDF and as a plain text file named nums.
Example File (file.txt):
Hello World!
Racecar
deified reviver
123+456=579
ROTATOR
42
See citation (150) in Chapter 3.789.
Time to repaper the wallpaper.
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CS2211 - Software Tools and Systems Programming Assignment #2
Example Output:
$ nums
Usage: nums options filename
$ nums 1
Error: no filename given!
$ nums 4 file.txt
Invalid option!
$ nums 1 badfilename
badfilename does not exist!
$ nums 0 file.txt
8
$ nums 1 file.txt
HELLO WORLD!
RACECAR
DEIFIED REVIVER
*+*=*
ROTATOR
*
SEE CITATION (*) IN CHAPTER *.*.
TIME TO REPAPER THE WALLPAPER.
$ nums 2 file.txt
Racecar
ROTATOR
$ nums 3 file.txt
789
579
456
150
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