Try your environment:

• Make sure you have access to the right version of your language. Pick the language you are currently learning from the below list:

  • Perl 5: As of this writing version 5.30 is already out, but most of the material will work on 5.10 and even 5.8, if you cannot upgrade. (See the most recent release of Perl 5.)

  • Raku (formerly known as Perl 6): See the most recent version of Raku (that was 2019.03 when I updated this).

  • Ruby: 2.5.x will be fine. Check out the most recent version of Ruby.

  • Python: In case you have Python 2 (e.g. 2.7.x) you should strongly consider switching to Python 3. Even though if you need to maintain legacy code then you might need to know Python 2 as well.

  • In the Python 3 series any of 3.8.x is the most recent, but most of the examples will work on older versions of Python 3 as well. See the most recent version of Python.

  • Go version go1.12.9 looks fine. The you could get the most recent version of Go.

• Check you can read the documentation.

• Check if you have a good editor with syntax highlighting.
• Write a simple script that prints "Hello world!".
• Add comments to your code.
• Add user documentation to your code.

Solutions

• Java

Calculate the area of a rectangular

Write a program that computes the area of a rectangular.

• Start by having two hard coded values. Multiply them and print the result. The result should be 42:

$ perl example.pl
42

• Then change the code to prompt the user for two numbers. Multiply them and print the result:

$ perl example.pl
First number: 7
Second number: 6
42

# ruby example.rb
First number: 3
Second number: 11
33

• Further modify the program to warn if one of the numbers given was negative.

$ python example.py
First number: 3
Second number: -1
Warning: Invalid input. The side of a rectangular cannot be negative.

Number guessing game

In this exercise we are starting to build a game, called the number guessing game.

The game is that the computer "thinks" about a number and we have to guess it. On every guess, the computer will tell us if our guess was smaller or bigger than the hidden number. The game ends when we find the number.

This exercise is the first step of this game.

Create a simple command line game guessing a whole number

1. Let the computer "think" about a whole number between 1-200.
2. Let the user guess a number.
3. Tell the user if his guess was bigger or smaller than the number the computer "thought" of or tell them if they hit the right number.
4. At this point the user only has one guess, though as a bounus you can allow the user to guess several times.

Solutions

• Number guessing in Ruby
• Number guessing in Python
• Number guessing in Perl 5
• Number guessing in Perl 6
• Number guessing in Groovy

Create calculator

Create a command line calucaltor that will prompt for two numbers and an operator and will calculate the result. Handle the following operators: +, -, *, and /.

An interaction should look like this:

$ mycalc
First number: 23
Second number: 19
Operator: +
Result: 42

where the numbers 23, 19 and the operator + are typed in by the user.

Solutions

• Java

Sum of numbers in a file

Let's implement something slightly useful.

In this exercise we have a file called numbers.txt that has numbers in it. Each line is a number.

Our aim is to add the numbers and print the result.

3
7
23
0
-17
98
12

Expected result is 126.

Tools

Some of the tools you might need to solve this exercise.

• Perl:

• Scalar values and variabels in Perl

• Numerical operators in Perl

• Open file in Perl

• Perl while loop

• Ruby:

• Open file and read content line-by-line in Ruby

• Convert string to number in Ruby

• For the advanced version:

• map in Ruby

• reduce in Ruby

• Python:

• Open file in Python

Solutions

• Python: sum of numbers
• Perl 5: sum of numbers in a file
• Ruby: sum of numbers in a file
• Groovy: sum of numbers

Analyze Apache log file - count localhost

In this exercise we take a log file generated by a web server, and do some simple analysis on it.

The file looks like this:

127.0.0.1 - - [10/Apr/2007:10:39:11 +0300] "GET / HTTP/1.1" 500 606 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:39:11 +0300] "GET /favicon.ico HTTP/1.1" 200 766 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
139.12.0.2 - - [10/Apr/2007:10:40:54 +0300] "GET / HTTP/1.1" 500 612 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
139.12.0.2 - - [10/Apr/2007:10:40:54 +0300] "GET /favicon.ico HTTP/1.1" 200 766 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:53:10 +0300] "GET / HTTP/1.1" 500 612 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET / HTTP/1.0" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET /style.css HTTP/1.1" 200 614 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET /img/machine-round.jpg HTTP/1.1" 200 17524 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.11 - - [10/Apr/2007:10:54:21 +0300] "GET /unix_sysadmin.html HTTP/1.1" 200 3880 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:51 +0300] "GET / HTTP/1.1" 200 34 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:51 +0300] "GET /favicon.ico HTTP/1.1" 200 11514 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:53 +0300] "GET /cgi/machine.pl HTTP/1.1" 500 617 "http://contact.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET / HTTP/0.9" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:27 +0300] "GET / HTTP/1.1" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:34 +0300] "GET /unix_sysadmin.html HTTP/1.1" 200 3880 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:45 +0300] "GET /talks/Fundamentals/read-excel-file.html HTTP/1.1" 404 311 "http://machine.local/unix_sysadmin.html" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"

Every row is a request on a web server. Some are pages, some are images, some are JavaScript files. That's not the important part now. Currently we are going to focus on the first field of every line which is the IP address of the requester. We go with a simple exercise.

As you might know, every device uses the IP address 127.0.0.1 to refer to itself. So visitors arriving from that IP address are based on the same machine.

The task is to write a scrip that will count how many requests came from 127.0.0.1 and how many from elsewhere?

Tools

• Perl 5: open the file for reading or die
• Perl 5: chomp remove trailing newlines
• Perl 5: index
• Perl 5: substr
• Ruby: ARGV command line parameters.
• Ruby: open a file for reading and iterate over it.

Solutions

• Perl 5 - Analyze Apache log file - count localhost
• Ruby - Analyze Apache log file - count localhost

Add more statistics

Take the solution from the count sum exercise where we added up the numbers in each row of a file, and add additional statistical values:

• minumum
• maximum
• average

If you are following the exercises then caluclating median and standard deviation might too difficult at this point, but you can give them a try.

Solutions

• Perl 5 - add more statistics

Write report to file

Take your solution from the Add more statistics exercise, and write the result into a file.

Tools

• Write to file in Perl (screencast) and writing to file in Perl (article)

Solutions

• Perl 5 - write report to file

Color selector

Given a list of colors (Blue, Yellow, Brown, White) create a script that will display a menu and ask the user to select one of the colors: For example an interaction would look like this:

$ perl color_selector.pl

Please select a number:
0) Blue
1) Yellow
2) Brown
3) White

2
The selected color is Brown

or like this:

$ perl color_selector.pl

Please select a number:
0) Blue
1) Yellow
2) Brown
3) White

7
Bad selection

Tools

• Arrays in Perl 5

Solutions

• Perl 5: Color selector, menu from array

Add numbers taken from a CSV file

Given a CSV file like this:

Tudor;Vidor;10;Hapci
Szundi;Morgo;7;Szende
Kuka;Hofeherke;100;Kiralyno
Boszorkany;Herceg;9;Meselo

Write a script that will take the values of the 3rd in this Comma Separated Values file and add them together.

Can your code also handle this file?

Budapest,Bukarest,1200,km
Tel Aviv,Beirut,500,km
London,Dublin,300,km
New York,"Moscow, East",6000,km
Local,"Remote
Location",10,km

Tools

• Perl 5 split
• Ruby split
• Ruby CSV

Solutions in Perl 5

• Perl 5 Process CSV file
• Perl 5 Process CSV file short version
• Perl 5 One-liner sum of column in CSV
• Process CSV file using Text::CSV_XS

Solution Ruby

• Reading CSV file in Ruby

Solution in Groovy

• Readng CSV file in Groovy

Improve the color selector

Improve the color selector

There are several parts of this exercise:

• The color selector created previously shows menu items numbered from 0. Change it so the displayed numbers will start at 1 but that it will still work correctly.
• Currently the user can give any value on the command line. Incluing "nonsense". Check that the given value is indeed one of the possible values hard-coded in the script. Report an error and quit if it isn't.
• Allow the user to supply a flag called --force If this flag is present allow any value as a color. Even "nonsense".
• Read the names of the valid colors from the colors.txt file.
• Allow the user to supply a --file flag as in "--file mycolor.txt" and take the name of the file with the colors from there.

Improve Number guessing game

This is an extension of the Number guessing game exercise.

This exercise has several steps.

First of all, let the user guess several times (with responses each time), until she finds the hidden number.

Allow various special keys too:

• n - skip the rest of this game (give up) and start a new game with new hidden number.
• s - show the hidden value (cheat).
• m - toggle: turn on/off move mode: When the move mode is on, after every guess the number can change by 2 in either direction.
• d - toggle: turn on / off debug mode. In debug mode show the hidden number every time before you are asked to supply the guess.
• x - exit

Now I can tell you that this is actually a 1 dimensional space fight. The number is your distance from the enemy space ship.

For training purposes limit the outer space to be between 0-200 so even when the move mode is on the space-ship won't fly off this area.

Finaly, keep track of the minimum and maximum score (number of guesses till hit) in a file.

Tools

Solutions

• Perl 5: Improve the number guessing game - multiple guesses
• Perl 5: Improve the number guessing game - exit
• Perl 5: Improve the number guessing game - s for show
• Perl 5: Improve the number guessing game - n for next game
• Perl 5: Improve the number guessing game - d for debug mode
• Perl 5: Improve the number guessing game - m for move mode

Count digits

Exercise: count digits in a file

Given a file like this, that has rows of numbers in it without anything, but a single space in between the numbers. Our task is to count how many times each digit appears.

23 34 9512341
3 34 2452345 5353 67 22
42136357013412
42 5 65 64 

Our expected output looks like this:

0 1
1 5
2 9
3 11
4 9
5 8
6 4
7 2
8 0
9 1

Tools for Perl 5

• <a href-"https://perlmaven.com/perl-tutorial">The Perl 5 tutorial in general.
• Perl 5: shift from @ARGV
• Perl 5: open a file for reading or die.
• Perl 5: Arrays
• Perl 5: chomp, remove trailing newlines.
• Perl 5: split, to cut a string into pieces.

Tools for Ruby

• Ruby: ARGV for command line parameters
• Ruby: Open file and read content
• Ruby: Arrays
• Ruby: Iterate over elements of a an array

Solutions

• Perl 5 count digits
• Ruby: count digits
• Groovy: count digits

Sort based on secondary condition

We have a file with strings in it. We would like to sort then according to length. The short strings first. The result is that within the strings of the same length we see them in random order. How can we sort them according to abc? So first come the short strings, but within each length we have abc order.

Foo
Foobar
Bar
Baz
Moo
Another
Reallylong
Shorter

Solutions

• Perl 5: How to sort based on secondary condition in Perl

Display unique rows of a file

Given a the following file:

A 1
B 2
A 2
C 3
B 2
D 4
C 1

Create another file in which the first character is unique:

A 1
B 2
C 3
D 4

Tools

Solutions

Sort mixed string

In a file we have the following strings: A1 B1 A27 A3 ... each string has a single letter at the beginning and then a number.

Sort them first based on the first letter and among values with the same leading letter sort them according to the numbers so the above values would be in the following order:

A1 A3 A27 B1

File:

A1 A27 C1 B1 B12 A38 B3 A3

Queue

The application should manage a queue of people.

• It will prompt the user for a new name by printing :.
• The user can type in a name and press ENTER.
• The app will add the name to the queue.
• If the user types in "n" then the application will print the first name in the queue.

A sample interaction will look like this:

: Foo
: Bar
: Moo
: n
  next is Foo
: n
  next is Bar
: Peter
: n
  next is Moo
: n
  next is Peter
: n
  the queue is empty

Check if number is prime

Write a program that gets a number on the commnad line a prints "True" if the number is a prime number or "False" if it isn't.

$ is_prime 42
False

$ is_prime 19
True

Implement Reverse Polish Calculator

Implement Reverse Polish Calculator

We are used to write calculations using the infix notation where the operator is between the two operands. e.g. 3 + 4 * 7. In order to implement a calculator that knows how to calculate this one needs to implement the order of operations.

In the Reverse Polish Notation the operator comes after the two operands. e.g. 3 4 + instead of 3 + 4.

In this notiation there are no preferences between operators.

The above expression can be written in RPN as:

3
4
7
*
+
=

The task is to implement RPN in your favorite language.

Python

In order to make it easer for you I've prepared a module that implements the low-level calculations.

def calc(a, op, b):
    '''
        from calc import calc
        calc(2, '+', 3)
    '''
    if op == '+':
        return a + b
    if op == '*':
        return a * b
    if op == '-':
        return a - b
    if op == '/':
        return a / b
    raise Exception("Operator '{}' not supported".format(op))


def test_calc():
    assert calc(2, '+', 3) == 5
    assert calc(2, '*', 3) == 6
    assert calc(8, '-', 3) == 5
    assert calc(8, '/', 2) == 4

    import pytest
    with pytest.raises(Exception) as exinfo:
        calc(2, '**', 3)
    assert exinfo.type == Exception
    assert str(exinfo.value) == "Operator '**' not supported"

# To test this module, run pytest calc.py

Solutions

• Python with list
• Python with deque
• Perl

Count words in a file

Similar to the exercise in which we counted digits, this time we would like to count words.

Give a file that contains lots of line, each line containig words separated by a space, we would like to count how many times each word appear. For the sake of simplicty in parsing, we can assume that there are no special pnctuations that we might need to get around. Just words separated by a space.

A small input file might look like this:

one word another word
a new sentence and a new word

Tools

Solutions

• Counting words in a file

Parse HTTP GET parameters

When you visit a web-site, fill in a form and submit it, in some cases you will see the URL containing a question mark ? followed by a long list of key-value pairs. These are the HTTP parameters of this GET request.

Every programming language has plenty of libraries handling these values properly, but we can also use them as an exercise.

So given a string like this: fname=Foo&lname=Bar&email=foo@bar.com or a string like this ip=127.0.0.1&machine=foobar create a hash/dictionary/associative array that will hold the key-value pairs found in the string.

Given fname=Foo&lname=Bar&email=foo@bar.com the data structure should look like this:

{
  'fname' : 'Foo',
  'lname' : 'Bar',
  'email' : 'foo@bar.com'
}

Given this string ip=127.0.0.1&machine=foobar the data structure should look like this:

{
  'ip'      : '127.0.0.1',
  'machine' : 'foobar'
}

For extra bonus try to handle this case as well:

Given fname=Foo&lname=Bar&email=foo@bar.com&email=here@there.or the data structure should look like this:

{
  'fname' : 'Foo',
  'lname' : 'Bar',
  'email' : [ 'foo@bar.com', 'here@there.or' ]
}

sort scores

Foo,23
Bar,70
Baz,92
Bozo,17
Gozo,52
Dardon,20
Mekodra,23

Bar      70
Baz      92
Bozo     17
Dardon   20
Foo      23
Gozo     52
Mekodra  23

Baz      92
Bar      70
Gozo     52
Foo      23
Mekodra  23
Dardon   20
Bozo     17

1234567890123456A001B0002D00004C0000051234567890123456
1234567890123456A001A002D00004C0000051234567890123456

if ARGV.length != 1
    puts "Usage: Needs filename"
    exit
end

fh = open ARGV[0]
fh.each do |line|
    if /REGEX/.match(line)
        print line
    end
end

#!/usr/bin/env python
from __future__ import print_function

import sys
import re

if len(sys.argv) != 2:
    print("Usage:", sys.argv[0], "FILE")
    exit()

filename = sys.argv[1]
f = open(filename, 'r')

for line in f:
    print(line, end=" ")

    match = re.search(r'REGEX1', line)
    if match:
       print("   Matching 1", match.group(0))

    match = re.search(r'REGEX2', line)
    if match:
       print("   Matching 2", match.group(0))

I    = 1
II   = 2
III  = 3
IV   = 4
V    = 5
VI   = 6
VII  = 7
VIII = 8
IX   = 9
X    = 10
...

I     = 1
V     = 5
X     = 10
L     = 50
C     = 100
D     = 500
M     = 1000

1.2.7.6
4.5.7.23
1.2.7
1.12.23
2.3.5.7.10.8.9 

09:20 Introduction
11:00 Exercises
11:15 Break
11:35 Scalars
12:30 Lunch Break
13:30 Exercises
14:10 Solutions
14:30 Break
14:40 Arrays
15:40 Exercises
17:00 Solutions
17:30 End

09:30 Advanced Arrays
10:30 Break
10:50 Exercises
12:00 Solutions
12:30 Hash fuction introduction
12:45 Lunch Break
14:15 Exercises
16:00 Solutions
16:15 Break
16:30 Subroutines
17:00 Exercises
17:30 End

09:20-11:00 Introduction
11:00-11:15 Exercises
11:15-11:35 Break
...

Lectures:  210 minutes 22%
Solutions:  95 minutes  9%
Break:      65 minutes  6%
...


Lectures: 
Introduction:  23 minutes 2%
...

# comment
[alpha]
 
base  = moon
ship= alpha 3
 
[earth]
   # ?
base=London   
ship=  x-wing

$VAR1 = {
          'earth' => {
                       'base' => 'London',
                       'ship' => 'x-wing'
                     },
          'alpha' => {
                       'base' => 'moon',
                       'ship' => 'alpha 3'
                     }
        };

$ wc *
      11      34     249 README.pod
       2       4     128 authors.txt
      37     110     773 check_examples.pl
wc: examples: read: Is a directory
    2737    2738   27627 python_weekly.pickle
wc: sites: read: Is a directory
       9      15     149 sites.yml
wc: static: read: Is a directory
    2796    2901   28926 total

$ find . | wc -l