Checklist 02

Here is a general outline of the key concepts and commands (arranged by topic) that you should know for Exam 02.

The exam will have the following format:

  1. Commands: Identify which command performs a certain task.

  2. Short Answers: Briefly answer questions about the Unix Philosophy and Software Installation.

  3. Debugging: Fix some simple shell scripts.

  4. Code Evaluation: Determine the results of commands involving cut, tr, grep, or sed.

  5. Filters: Use Unix filters to answer some questions.

  6. Scripting: Write a shell script that utilizes command line arguments and filters.

Parts 5 and 6 can be done with the aid of your laptop and the Internet (but not other people). Parts 1 through 4 is to be done first on paper.

Software Installation

Concepts

  1. What is the purpose of an installer? What sort of things does this type of program do (identify at least three things)?

  2. What is a package manager and why do many Unix systems use them?

  3. When do you need administrator priviledges to install software?

  4. How would you use configure and make to install software to your $HOME directory? What environment variables would you need to update to ensure you can execute the program you installed? Use the libraries?

Commands

  1. tar

  2. unzip

  3. sudo

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)?

  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

    8. trap

  3. How do you debug a shell script? What different modes do we have to help us figure out what a script is doing?

Commands

  1. sh

  2. test

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 file is readable!
done

Scripting

Write the following shell script:

$ ./column.sh -h
usage: column.sh [-n N -d D -S -R] column

    -n N    Number of items to display (default is 5).
    -d D    Delimiter to use (default is ",").
    -S      Sort output.
    -R      Randomize output.

This script selects a column (default is 1) from the CSV input and then
displays the first N items.

Examples:

$ ./column.sh -d : < tmnt.txt
Leonardo
Donatello
Raphael
Michelangelo

$ ./column.sh -d : -n 1 < tmnt.txt
Leonardo

$ ./column.sh -d : -n 1 3 < tmnt.txt
katana

$ ./column.sh -d : -S 3 < tmnt.txt
bo
katana
nunchucks
sai

$ ./column.sh -d : -R 3 < tmnt.txt
nunchucks
katana
sai
bo

Note: The tmnt.txt file is described below.

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? What do they do and how are they related to the Unix Philosophy?

Commands

  1. cut

  2. sort

  3. uniq

  4. shuf

  5. tr

  6. grep

  7. sed

  8. head

  9. tail

  10. awk

Sample Questions

Given the file tmnt.txt, which contains:

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

Code Evaluation

What is the result of the following shell commands?

  1. cut:

    1. echo "Leonardo,Donatello,Raphael,Michelangelo" | cut -d , -f 1

    2. echo "Leonardo,Donatello,Raphael,Michelangelo" | cut -d , -f 1,3

    3. echo "Leonardo,Donatello,Raphael,Michelangelo" | cut -d , -f 2-

    4. echo "Leonardo,Donatello,Raphael,Michelangelo" | cut -b 1,15,39

  2. tr:

    1. echo "Pizza! Pizza!" | tr '!' '?'

    2. echo "Pizza! Pizza!" | tr 'iaz' '145'

    3. echo "Pizza! Pizza!" | tr -d '[n-z]'

    4. echo "Pizza! Pizza!" | tr -d '[:punct:]'

  3. grep:

    1. cat tmnt.txt | grep '^[LM]'

    2. cat tmnt.txt | grep 'e.*o'

    3. cat tmnt.txt | grep -Eo '^[^: ]+'

    4. cat tmnt.txt | grep -Eo '[a-zA-Z]+[al]{2}[^:]*'

  4. sed:

    1. cat tmnt.txt | sed -nr 's/Leonardo/Splinter/p'

    2. cat tmnt.txt | sed -r '/lo/d'

    3. cat tmnt.txt | sed -nr 's|.*:o([^: ]+).*|O\1|p'

    4. cat tmnt.txt | sed -nr 's/.*([LD][^:]+)[: ]+([^:]+).*/\2/p'

Filters

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