COURSE 2 – USING PYTHON TO INTERACT WITH THE OPERATING SYSTEM

Module 6: Bash Scripting

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TABLE OF CONTENT

INTRODUCTION – Bash Scripting

In this module, you’ll be exposed to what the Linux OS has to offer and you’ll learn about Bash scripting. We’ll go over basic Linux commands and explore the many processes Linux has to offer, including a key concept called redirection. We’ll then deep dive into creating bash scripts using variables and globs. Finally, we’ll learn about advanced bash concepts and develop an understanding of when to use bash versus Python.

Learning Objectives

  • Use basic Linux commands to work with files and directories
  • Create bash scripts and execute them
  • Execute scripts using variables and globs to influence the output of these scripts
  • Utilize while and for loops in bash scripts
  • Describe when it’s necessary to use Bash scripts over Python scripts

PRACTICE QUIZ: INTERACTING WITH THE COMMAND LINE

1. Which of the following commands will redirect errors in a script to a file?

  • user@ubuntu:~$ ./calculator.py < error_file.txt
  • user@ubuntu:~$ ./calculator.py 2> error_file.txt (CORRECT)
  • user@ubuntu:~$ ./calculator.py > error_file.txt
  • user@ubuntu:~$ ./calculator.py >> error_file.txt

You nailed it! The “2>” sign will redirect errors to a file.

2. When running a kill command in a terminal, what type of signal is being sent to the process?

  • SIGTERM (CORRECT)
  • SIGSTOP
  • SIGINT
  • PID

You got it! The kill command sends a SIGTERM signal to a processor ID (PID) to terminate.

3. What is required in order to read from standard input using Python?

  • echo file.txt
  • cat file.txt
  • The file descriptor of the STDIN stream
  • Stdin file object from sys module (CORRECT)

Right on! Using sys.stdin, we can read from standard input in Python.

4. _____ are tokens delivered to running processes to indicate a desired action.

  • Signals (CORRECT)
  • Methods
  • Functions
  • Commands

Nice job! Using signals, we can tell a program that we want it to pause or terminate, or many other possible commands.

5. In Linux, what command is used to display the contents of a directory?

  • rmdir
  • cp
  • pwd
  • ls (CORRECT)

Nice job! The ls command lists the file contents of a directory.

6. Which of the following Linux commands will create an empty file?

  • touch (CORRECT)
  • pwd
  • mkdir
  • cd

Right on! The touch command will create an empty file.

7. How do you append the output of a command to a .txt file?

  • user@ubuntu:~$ ./calculator.py > result.txt
  • user@ubuntu:~$ ./calculator.py >> result.txt (CORRECT)
  • user@ubuntu:~$ ./calculator.py < result.txt
  • user@ubuntu:~$ print("This will append") 

Great work! A double greater than sign will append a command output to a file.

8. Which of the following is the correct way of using pipes?

  • user@ubuntu:~$ cat sample.txt ./process.py
  • user@ubuntu:~$ cat sample.txt || ./process.py
  • user@ubuntu:~$ tr ' ' '\n' | sort | cat sample.txt
  • user@ubuntu:~$ cat sample.txt | tr ' ' '\n' | sort (CORRECT)

Woohoo! The contents of the txt file are passed on to be placed in their own line and sorted in alphabetical order on the display.

9. What can you type in the terminal to stop the traceroute command from running cleanly?

  • Ctrl-C
  • SIGINT (CORRECT)
  • Ctrl-Z
  • SIGSTOP

Right on! This sends a SIGINT signal to the program to stop processing cleanly.

PRACTICE QUIZ: BASH SCRIPTING

1. Which of the following commands will output a list of all files in the current directory?

  • echo * (CORRECT)
  • echo a*
  • echo *.py
  • echo ?.py

Right on! The star [*] globe will echo or output all files in the current directory.

2. Which module can you load in a Python script to take advantage of star [*] like in BASH?

  • ps
  • stdin
  • Glob (CORRECT)
  • Free

Woohoo! The glob module must be imported into a Python script to utilize star [*] like in BASH. 

3. Conditional execution is based on the _____ of commands.

  • environment variables
  • parameters
  • exit status (CORRECT)
  • test results

Nice job! In Bash scripting, the condition used in conditional execution is based on the exit status of commands.

4. What command evaluates the conditions received on exit to verify that there is an exit status of 0 when the conditions are true, and 1 when they are false?

  • test (CORRECT)
  • grep
  • echo
  • export

Great work! test is a command that evaluates the conditions received and exits with zero when they’re true and with one when they’re false.

5. The opening square bracket ([), when combined with the closing square bracket (]), is an alias for which command?

  • glob
  • test (CORRECT)
  • export
  • if

Right on! The test command can be called with square brackets ([]).

6. Which command will correctly run a bash script?

  • user@ubuntu:~$ #!/bin/bash
  • user@ubuntu:~$ ./bash.py 
  • user@ubuntu:~$ ./bash_sample.sh (CORRECT)
  • user@ubuntu:~$ ./sh.bash

Right on! A bash script is run with the .sh file extension.

7. When defining a variable you receive the “command not found” message. Which of the following commands will resolve this error?

  • User1= billy
  • $User2 =billy
  • User3 = $billy
  • User4=billy (CORRECT)

Great work! The variable “User4” has a value of “billy”.

8. A conditional block in Bash that starts with ‘if’, ends with which of the following lines?

  • fi (CORRECT)
  • if
  • else
  • grep

Right on! The if conditional ends with fi (a backwards “if”).

PRACTICE QUIZ: ADVANCED BASH CONCEPTS

1. Which command does the while loop initiate a task(s) after?

  • while
  • n=1
  • done
  • do (CORRECT)

Awesome! Tasks to be performed are written after do.

2. Which line is correctly written to start a FOR loop with a sample.txt file?

  • for file in sample.txt; do (CORRECT)
  • for sample.txt do in file
  • do sample.txt for file
  • for sample.txt in file; do

You nailed it! The contents of sample.txt are loaded into a file variable which will do any specified task.

3. Which of the following Bash lines contains the condition of taking an action when n is less than or equal to 9?

  • while [ $n -le 9 ]; do (CORRECT)
  • while [ $n -lt 9 ]; do
  • while [ $n -ge 9 ]; do
  • while [ $n -ot 9 ]; do

Right on!. This line will take an action when n is less than or equal to 9.

4. Which of the following statements are true regarding Bash and Python? [Check all that apply]

  • Complex scripts are better suited to Python. (CORRECT)
  • Bash scripts work on all platforms.
  • Python can more easily operate on strings, lists, and dictionaries. (CORRECT)
  • If a script requires testing, Python is preferable. (CORRECT)

Nice work! When a script is complex, it’s better to write it in a more general scripting language, like Python.

Awesome! Bash scripts aren’t as flexible or robust as having the entire Python language available, with its many different functions to operate on strings, lists, and dictionaries.

Right on! Because of the ease of testing and the fact that requiring testing implies complexity, Python is preferable for code requiring verification.

5. The _____ command lets us take only bits of each line using a field delimiter.

  • cut (CORRECT)
  • echo
  • mv
  • sleep

Excellent!  The cut command lets us take only bits of each line using a field delimiter.

6. Which “for” conditional line will add users Paul and Jeremy to a user variable?

  • for users in Paul Jeremy
  • for user in Paul Jeremy (CORRECT)
  • for Paul Jeremy in user
  • for Paul & Jeremy in user

Nice job! The elements Paul and Jeremy are added to the user variable.

7. When using the following command, what would each line of the output start with?

user@ubuntu:~$ tail /var/log/syslog | cut -d' ' -f3-

  • CRON[257236]:
  • October
  • 31
  • 10:18:41 (CORRECT)

Woohoo! The time of the log will be shown with the -f3- or field three option of the cut command.

8. Which of the following statements would make it better to start using Python instead of Bash?

  • Operate with system commands.
  • Use on multi-platforms. (CORRECT)
  • Operate with system files.
  • Run a single process on multiple files.

Right on! It is better to use Python and its standard library to use when working across multiple platforms.

EDIT FILES USING SUBSTRINGS

1. In Linux, what does the cat command allow you to do?

  • Extract a given number of characters or columns from a file. 
  • Process text line-by-line and print any lines that match a specified pattern.
  • Create single or multiple files, view the contents of a file, concatenate files, and redirect output in the terminal or other files. (CORRECT)
  • Search text and match a string or pattern within a file.

Correct

2. What is a delimiter? 

  • A target file
  • A text string containing characters 
  • A character or set of characters that separate text strings (CORRECT)
  • A file location

Correct

3. A single greater than sign (>) or a double greater than sign (>>) can be used to redirect standard output. What do commands with a single greater than sign (>) do with existing file content? 

  • Delete the file content 
  • Overwrite the file content (CORRECT)
  • Append the file content
  • Duplicate the file content

Correct

4. A peer asks which Linux command she should use to process text line-by-line and print the lines that match a specified pattern, such as a file directory. What do you tell her?

  • The cat command
  • The grep command (CORRECT)
  • The cut command
  • The overwrite command

Correct

5. What is the difference between a command that ends with -f 1-3 and a command that ends with -f 1,3?

  • The first specifies fields 1 and 3 and the second specifies fields 1 through 3.
  • There is no difference.
  • The first specifies fields 1 through 3 and the second specifies fields 1 and 3. (CORRECT)
  • The first is a cut command and the second is a cat command.

Correct

6. On Unix-like operating systems, the command test is a command-line utility that evaluates conditional expressions. In the following command, what does the flag “-e” after “test” do? 

if test -e ~/data/jane_profile_07272018.doc; then echo "File exists"; else echo "File doesn't exist"; fi

  • This flag checks if the file jane_profile_07272018.doc is present in the file system. (CORRECT)
  • This flag deletes files including “jane”, “profile”, and “07272018” in the file system. 
  • This flag checks if the profile “jane” is present in the file 07272018.doc. 
  • This flag returns a list of all files including “jane”, “profile”, or “07272018” in the file system. 

Correct

7. After you created the text file oldFIels.txt and stored the “jane” lines there, what command let you view the contents of the newly generated file?

  • > oldFiles.txt
  • cat oldFiles.txt (CORRECT)
  • nano oldFiles.txt
  • chmod oldFiles.txt

Correct

8. Bash script allows three different iterative statements:, or “loops”. What is a “while” loop?

  • The execution of a group of statements over a control condition.
  • The execution of a set of instructions as long as the control condition remains false.
  • The execution of a set of instructions as long as the control condition remains true. (CORRECT)
  • The execution of a set of instructions as long as the control condition is specified.

Correct

9. A junior programmer has asked your advice on which Linux command to use to create single or multiple files, view the contents of a file, concatenate files, and redirect output in terminal or other files. Which Linux command would you tell them to use?

  • The cut command
  • The overwrite command
  • The cat command (CORRECT)
  • The grep command

Correct

10. What is the Linux command you should use to extract certain specific information columns from a larger database? 

  • The cut command (CORRECT)
  • The cp command
  • The grep command
  • The cat command

Correct

11. What will executing the command grep ‘jane’ ../data/list.txt do?

  • Return all lines containing the text string “jane” in the file list.txt. (CORRECT)
  • B: Create a target file named jane.list.txt.
  • Delete all lines containing the text string “jane” in the file list.txt.
  • Cut all lines containing the text string “jane” in the file list.txt.

Correct

12. What will the command cd data do? 

  • Navigate to the data directory. (CORRECT)
  • Duplicate the data directory. 
  • List the contents of the data directory. 
  • Copy the data directory.

Correct

13. Looking at the following command, how might you predict the fields in the file list.txt are delineated? 

grep " jane " ../data/list.txt | cut -d '...' -f 1

  • There is nothing to delineate the fields.
  • By an ellipsis (…)(CORRECT)
  • By a forward slash (/)
  • By a hyphen (-)

Correct

14. In Bash scripting, there are three primary iterative statements, commonly referred to as loops. Among these is the “until” loop. What is the purpose of the “until” loop?

  • The execution of a set of instructions as long as the control condition is specified.
  • The execution of a set of instructions as long as the control condition remains false. (CORRECT)
  • The execution of a set of instructions as long as the control condition remains true.
  • The execution of a group of statements over a set of items. 

Correct

15. When using the cut command, when is the -d option needed?

  • When fields are separated by delimiters (CORRECT)
  • When there are text strings 
  • When there is a set of fields 
  • When there is a range of fields

Correct

16. Which command should you use to check if a particular file is present in the file system?

  • The cut command
  • The overwrite command
  • The cat command
  • The test command (CORRECT)

Correct

17. While preparing to catch all “jane” lines and store them in a text file called oldFiles.txt, you had to create that file. Which of the following commands did you use to create oldFiles.txt? 

  • > oldFiles.txt (CORRECT)
  • # oldFiles.txt
  • cd ~/oldFiles.txt
  • >> oldFiles.txt

Correct

18. Bash script allows three different iterative statements:, or “loops”. What is a “for” loop?

  • The execution of a group of statements over a set of items. (CORRECT)
  • The execution of a set of instructions as long as the control condition remains false.
  • The execution of a set of instructions as long as the control condition remains true.
  • The execution of a set of instructions as long as the control condition is specified.

Correct

19. A software developer has been asked to extract the name, phone number, and address columns from a file that contains over 2,000 lines of customer data. Which of the following Linux commands should the developer use?

  • The cp command
  • The cut command (CORRECT)
  • The grep command
  • The cat command

Correct

20. A single greater than sign (>) or a double greater than sign (>>) can be used to redirect standard output. What do commands with a double greater than sign (>>) do with existing file content? 

  • Append the file content (CORRECT)
  • Overwrite the file content 
  • Duplicate the file content 
  • Delete the file content

Correct

21. The redirection commands cat > [file] and cat >> [file] are used to redirect standard output to a target file. What happens if that target file doesn’t exist?

  • The redirection command will be terminated. 
  • A new file with the same name will be created. (CORRECT)
  • Append file content in the existing file.
  • An input/output error will be returned.

Correct

22. Complete this sentence. The Linux command you should use to create single or multiple files, view the contents of a file, concatenate files, and redirect output in the terminal or other files is the ____command. 

  • cat (CORRECT)
  • grep 
  • overwrite 
  • cut

Correct

23. The grep command is an acronym: What does grep stand for? 

  • global regular expression process
  • global regular expression print (CORRECT)
  • global regular extraction process 
  • global regular expression pattern

Correct

24. What will executing the command cat list.txt do?

  • Amend the fields in the file list.txt.
  • Show the contents of the file list.txt. (CORRECT)
  • Duplicate the file list.txt.
  • Concatenate the fields in the file list.txt.

Correct

CONCLUSION – Bash Scripting

In conclusion, this module provides a comprehensive exploration of the Linux operating system, introducing you to the intricacies of Bash scripting. The curriculum encompasses fundamental Linux commands, an in-depth look at diverse Linux processes with a focus on the crucial concept of redirection.

Moving forward, you will engage in the creation of Bash scripts, incorporating essential elements such as variables and globs. The module concludes by delving into advanced Bash concepts, cultivating a nuanced understanding of when to opt for Bash over Python in your scripting endeavors.

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