Checklist 01

Here is a general outline of the key concepts and commands (arranged by topic) that you should know for Exam 01.

The exam will have the following format:

1. Commands: Identify which commands perform certain tasks (multiple-choice).

2. Shell and Files: Identify ways to perform certain tasks in the shell (multiple-choice).

3. Networking and Processes: Identify ways to perform networking and process management tasks (multiple-choice).

4. Pipelines: Describe pipelines, I/O redirection, and the Unix Philosophy (multiple-choice, fill-in-the-blank).

5. Shell Scripting: Debug, fix, and evaluate a shell script (multiple-choice, fill-in-the-blank).

6. Filters: Use Unix filters to answer some questions (coding on the computer).

All portions of the exam will take place online. Parts 1 through 5 will be an online quiz while Part 6 will require submitting code to your assignments repository.

Introduction¶

Concepts¶

• What is Unix?

• What is a shell?

• How would do you use git to:

  • Create a copy a repository.

  • Create a new branch.

  • View the changes you've made.

  • Save a change you've made.

  • Share the changes you've made.

  • Retrieve the changes from a remote location.

• What are aliases?

  You should know how to create one and how you would make them persistent (ie. survive the current shell session).

• What are environment variables?

  You should know how to set and modify them. In particular, you should be familiar with the PATH environment variable and know what it controls.

Commands¶

1. git

   Version control system for managing our files.

Sample Questions¶

1. Which environmental variable does the shell search to locate an executable?

   • APPS
   • HOME
   • PATH

   • PROGRAMS

2. How would you create a new checklist01 branch off the latest master branch?

Files¶

Concepts¶

• What is the general layout or hierarchy of a typical Unix filesystem?

  You should be familiar with the most common directories found in a typical Unix filesystem (e.g. /bin, /etc, /lib, /usr, /tmp, /var, etc.).

• What is the difference between an absolute and relative path?

  You should know how to reference a file using both methods.

• How do Unix file permissions work? How would you set them to restrict access for certain operations and certain classes?

  You should be able to translate from octal to rwx triplets and back.

• What is the difference between a hard link and a soft link?

  You should know the command to create both.

Commands¶

1. ls

   List the contents of a directory (long, human-readable, sorted)

2. chmod

   Set permissions using octal and symbolic arguments.

3. stat

   View the inode information for a file.

4. du

   View the total disk usage for a file or directory.

5. ln

   Create hard and soft links.

6. find

   Search directory for files by name and type.

Sample Questions¶

1. Which of the following commands makes a file executable?

   • chmod +x file
   • stat file
   • make file

   • test -x file

2. Which of the following commands shows the meta-data of a file?

   • ls -l file
   • stat file
   • du file

   • find file

Process¶

Concepts¶

• What is a process? What attributes does it have?

  You should know at a high-level the typical attributes of a process (ie. PID, UID, etc.).

• What does it mean to signal a process? What do different the different signals do (TERM, INT, KILL)?

  You should know the difference between terminating a process gracefully and terminating it forcefully.

• How do we suspend, foreground, and background a process?

  You should know the appropriate keybindings and commands to perform these actions.

Commands¶

1. ps

   List the processes for the current user and for the whole system.

2. top

   Interactively view and manage processes.

3. kill

   Signal a process by PID.

4. time

   Measure how long it takes a process to execute.

5. pkill

   Signal a process by name.

Sample Questions¶

1. Which of the following commands forcefully terminates a process?

   • kill PID
   • kill -9 PID
   • sudo kill PID

   • kill -KILL PID

2. Suppose we were running cat. How would we signal to the program that we are done inputting text?

   • Control-Z
   • Control-I
   • Control-D

   • Control-C

I/O Redirection¶

Concepts¶

• What three files does every process start with?

• How do you redirect the output of a command into a new file?

• How do you redirect the output of a command and append it to a file?

• How do you redirect the output of one command as the input to another?

• How do you direct the contents of a file into the input of command?

• What is /dev/null? How would you use it to output stderr but ignore stdout of a program?

• What is a here document and how would you use it?

Commands¶

1. tee

   Redirect stdin to both stdout and a file.

2. write

   Write to another users terminal.

Sample Questions¶

1. Which of the following pipelines counts all the "Permission denied" errors encountered when recursively searching file names under the "/etc" directory?

   • find /etc > /dev/null | wc -l
   • find /etc 2>&1 > /dev/null | wc -l
   • find /etc 2> /dev/null | wc -l

   • find /etc > /dev/null 2>&1 | wc -l

2. Which of the following appends the standard output of a program to a file?

   • program > output
   • program 2> output
   • program >> output

   • program &> output

Networking¶

Concepts¶

• What is bandwidth and latency?

  You should know what each measures and what programs we would use to perform these measurements.

• What is an IP address? How is a domain name related to it?

  You should know the commands to lookup this information.

• What is a network port?

  You should know how to scan for ports and how to connect to a machine at a specific a domain or address and port number.

Commands¶

1. ip / ifconfig

   List the IP addresses of the current machine.

2. nmap

   Scan remote machine for open ports.

3. nc

   General purpose tools to communicate with TCP-based network services.

4. curl

   Communicate using HTTP (ie. download files from the web).

5. ping

   Measure the latency from host to remote machine.

Sample Questions¶

1. Which of the following commands can be used to measure bandwidth?

   • wget URL
   • ping URL
   • nmap URL

   • curl URL

2. Which of the following statements are true (select all that apply)?

   • Every domain name translates to at least one IP address.
   • Every IP address is publically accessible.
   • Every IP address maps to exactly one domain name.

   • Every device has an IP address of 127.0.0.1.

Shell Scripting¶

Concepts¶

1. What is a shell script? What is a she-bang and why do we need it (or what does it do)?

   You should understand how a shell script is interpreted and the impact the she-bang has on this interpretation. You should also know how to execute a shell script.

2. You should know the basics of the shell programming language:

   1. variables

   2. capturing STDOUT

   3. if statement

   4. case statement

   5. for loop

   6. while loop

   7. function

3. How do we parse command line arguments in a shell script?

Commands¶

1. sh

   Bourne shell interpreter.

2. test

   Perform checks on file types and values.

3. tar

   Extract or compress tarballs.

4. seq

Sample Questions¶

Debugging¶

The following scripts contain errors. Identify and correct all the bugs.

1. This script checks each file passed via command line arguments and reports if the file is readable.

   for $file in '$@'; do
       [-r $file] | echo file is readable!
   done
   

2. This script checks each file passed via command line arguments and reports if the file is readable.

   is_readable() {
       test -r $@
   }
   
   while (-n "$#"); do
       is_readable("$@") | echo $@ is readable!
   
   done
   

Filters¶

Concepts¶

1. What are the three tenets of the Unix Philosophy?

2. What are regular expressions?

   You will need to know the basic metacharacters such as

   • .
   • *
   • []
   • [^]
   • ^
   • $
   • ()
   • |
   • \n

   • {m, n}

   You will also need to be familiar with the basic character classes and their character set equivalents such as:

   • [:alpha:] = [a-zA-Z]
   • [:lower:] = [a-z]
   • [:upper:] = [A-Z]
   • [:space:] = [ \t\r\n\v\f]

   • [:digit:] = [0-9]

3. What are filters?

   You should be familiar with the general idea of a filter and know how to use specific tools for certain tasks.

Commands¶

1. cut

   Extract fields or characters.

2. sort

   Order text.

3. uniq

   Remove duplicates.

4. tr

   Translate from one set of characters to another.

5. grep

   Search based on pattern.

6. sed

   Search and replace or extract text based on regular expressions.

7. head

   Display first few lines of input.

8. tail

   Display last few lines of input.

Sample Questions¶

Given the file tmnt.txt, which contains:

Leonardo:blue:katana
Donatello:purple:bo
Raphael:red:sai
Michelangelo:orange:nunchucks

Given the tmnt.txt file above, write Unix pipelines that perform the following tasks:

• List only the names of the turtles in sorted order.

• List only the colors of the turtles in sorted order.

• List only the weapons of the turtles in sorted order.

• List only the turtles whose names end in lo.

• List only the turtles with last names that contain two consecutive vowels.

• Count how many colors begin with a b.

• Count how many colors end with an e.

• List only the turtles names whose name ends with a vowel and whose weapon ends with a vowel.

• List only the turtles names with two of the same consecutive letter (i.e. aa, bb, etc.)

• List the colors that don't end with a vowel.

• List the weapons that contains a repeat letter anywhere in the string.