Description

COMP2113 Programming Technologies Module 1 Checkpoint Exercise
Name:

Instructions:
For each single question or each group of questions in the Checkpoint exercise, please type your answer right after the question in this Word document. Please refer to the example below.
Checkpoint 0:

Checkpoint 1.1
Now, let’s try to answer the following questions. Although you haven’t been taught the meaning of the following commands, you can display the manual page of these commands and learn their meanings by yourself
1. Why do we need to learn command line although we can use a GUI to control a computer? Not all computers come with a GUI, or other reasonable answer
2. What is the meaning of ls -t?
It lists the contents in the current working directory.
3. What is the meaning of the command pwd? prints the name of the present working directory.
4. What is the meaning of the command rm?
Removes a file
5. What is the meaning of the command mv?
Can be used to rename a file/directory or moves a file to the defined directory
6. Suppose that the fileA does not exist in your present working directory, what is the meaning of the command touch fileA?
Creates an empty file called fileA
7. What is the meaning of the command tar?
Tar is used to create a compressed file in the format gzip
8. What is the command for creating an archive files.tar from two files named fileA and fileB?
tar -cvf files.tar fileA fileB

Checkpoint 1.2a
Assume we have logged in Ubuntu and started a bash shell. The current directory is the home directory, i.e., ~ . We want to perform the following tasks sequentially. For each of the tasks below, please state the shell command(s) used to perform it.
1. Create a new subdirectory “assignments” under ~.
mkdir assignments
2. Create a new subdirectory “assignment 1” under “assignments”. (Note that we are creating one subdirectory
“assignment 1” but not two subdirectories “assignment” and “1” ) cd assignment
mkdir “assignment 1”
3. Remove the directory “assignments” and all its subdirectories.
rm -rf assignments

Checkpoint 1.2b
[Self-learning question] – You need to search for the information on the Internet to answer this question.
There is another way to modify the permission, which is called the Absolute mode.

a. Explain the meaning of chmod 666 hello.txt
In Absolute mode, the meaning of “666” is to set read and write permissions to all the users
b. Explain the meaning of chmod 700 hello.txt
It is to set read, write and execute permissions for owner and no permissions for group and others
c. What is the chmod command, in absolute mode, to set the following permission for hello.txt?
User permissions Group Permission Other permission
r w x – w – r – –
chmod 724 hello.txt
d. The administrator says that “One does not simply 777 their entire server”, explain what the problem is if we chmod 777 for all the files.

Checkpoint 1.3
Consider the two files below:
$cat question1A
Apple
Boy
Cat
Dog
Egg $cat question1B
Boy
Cat
Egg

Note that file question1B is created by removing “Apple” and “Dog” from the file question1A.
A. What will be the output if we execute the following command (Please try to think about the output before trying it in the shell)? Please explain your answer.
$diff question1A question1B
The first and the fourth line of question1A will be deleted. Meanwhile, the line “Boy” and line “Egg” will be moved up one line separately.
B. What will be the output if we execute the following command (Please try to think about the output before trying it in the shell)? Please explain your answer.
$diff question1B question1A
“Apple” will be added after line 0 of question1B (after this step, question1B will have four lines in total).
Then “Dog” will be added after line 3 of question1B (the file will have five lines now).

Checkpoint 1.4
This is a challenging exercise! You need to understand the shell commands and the techniques introduced in the previous sections to work on this task.
The following C++ program gen4.cpp reads in a 4-character string from the input and generates all possible permutations from the 4 characters.
//gen4.cpp
#include <iostream> #include <string> int main() { std::string s; std::cin >> s; for (int i = 0; i < s.length(); i++) {
for (int j = 0; j < s.length(); j++) { for (int k = 0; k < s.length(); k++) { for (int l = 0; l < s.length(); l++) {
if (i != j && i != k && i != l && j != l && j != k && k != l) { std::cout << s[i] << s[j] << s[k] << s[l] << std::endl;
}
}
}
}
}
return 0; }

To compile gen4.cpp
$ g++ gen4.cpp -o gen4

The input of the program should be stored in the file gen4_input.txt with the following content.

gen4_input.txt

1. Give ONE command (one line of command(s)) to run the gen4 with gen4_input.txt as input and redirect the result to a file named gen4_output.txt.
Hints:
$ [your_command] $ cat gen4_output.txt lopo loop lpoo lpoo
…
$ wc gen4_output.txt
24 24 120 gen4_output.txt
*The output file should contain all permutations of the letters ‘l’, ‘o’, ’p’ and ‘o’. There should be 24 permutations in total.
$ ./gen4.o < gen4_input.txt > gen4_output.txt

2. Give ONE command to sort the words in gen4_output.txt in alphabetical order, and then also remove the adjacent duplicate lines and finally store the result in a file named sort_uniq.txt.
Hints: Consider the command uniq
$ [your command] $ cat sort_uniq.txt.
loop lopo lpoo olop olpo oolp oopl oplo opol
ploo polo pool
$ wc sort_uniq.txt
12 12 60 sort_uniq.txt
*There should be 12 unique words total.
$sort gen4_output.txt | uniq > sort_uniq.txt
3. Give ONE command to check the spelling in sort_uniq.txt and store the misspelled words into another file named misspell.txt.
$spell sort_uniq.txt > misspell.txt
4. Now sort_uniq.txt contains all distinct generated words, and misspell.txt contains all misspelled words. The differences between the two files are the meaningful 4-character words. Give ONE command to return the correctly spelled words as shown below:
$ [your command]
< loop
< polo
< pool
Hints: Consider the command diff and grep. diff sort_uniq.txt misspell.txt | grep -E ‘[a-z]{4}’

Checkpoint 1.5
Consider the file question1.txt.
2011111111,John,M,98
2011222222,Marry,F,85
2011333333,Sally,F,85
2012111111,Kit,M,86
2012222222,Ben,M,97
2012333333,Smitty,F,92
2012444444,Jolly,F,93
2012555555,Ken,M,100
Figure 1 question1.txt 1. Give ONE command to return the lines that contain the record of Kit Hints:
$ [Your command]
2012111111,Kit,M,86
grep “Kit” question1.txt

• Give ONE command to find the students with UID begin with “2012” (i.e., To find the lines that begin with 2012) Hints:
$ [Your command]
2012111111,Kit,M,86
2012222222,Ben,M,97
2012333333,Smitty,F,92
2012444444,Jolly,F,93
2012555555,Ken,M,100
grep -E “^2012” question1.txt

• Give ONE command to return the lines that contain the record of the students who are both:
• UID start at 2012, and
• Name starts with the characters J or S
Hints:
$ [Your command]
2012333333,Smitty,F,92
2012444444,Jolly,F,93

grep -E “^2012.*,[JS]” question1.txt