• Materials marked as "optional" can be skipped.
  • The first two weeks contain more materials than the later weeks, because I am assuming that you are already familiar with basic programming concepts from other programming languages.
  • Starting from week 4, you will be working with HTML. If you have never manually edited HTML pages, I would recommend that you familiarize yourself with HTML tags before week 4. See the resources for week 1 on the module webpage.

    1 A first example "Hello World"

    #!/usr/local/bin/perl -w
    # This program says "hello" to the world
    print "Hello World!\n";

    Telnet to a Unix computer. Copy the blue text from the screen and paste it into a file. Save the file, for example, under the name "hello". Then type at the Unix prompt:

    perl hello

    1.1 Explanations

    # indicates a comment; the line is ignored
    print a command; prints the string between the quotes
    \n newline character
    ; indicates the end of a command

    1.2 Exercises

    1) Add a second print statement to the script from the example. (For example print "How are you?".) What does adding or deleting "\n" change?

    2) Make some random changes, for example, delete the "#" before "This program says ..."; delete the semicolon after "World\n"; etc. In most cases you will get an error message. The only useful piece of information in that message is probably the number of the line in which the error occurred. Fix the errors until the script executes again successfully.

    3) Type "perl -v" at the command line. It gives you information about the specific version of Perl that is installed on the computer.
    Type "perldoc perl" at the command line. To exit "perldoc perl" type "q". Perldoc provides on-line help pages. (Don't try to read the documentation right now - it's too technical. Just keep in mind that it's there in case you need it later in the semester.) If perldoc is not installed on a machine, try "man perl".

    2 A second example

    #!/usr/local/bin/perl -w
    # A program for greeting people
    print "What is your name? ";
    $name = <STDIN> ;
    chomp ($name);
    print "Hello, $name! How are you?\n";

    2.1 Explanations

    $name a variable for a "name"
    = an assignment operator
    <STDIN> reads from standard input (i.e. keyboard)
    chomp deletes the newline character ("enter" key)

    2.2 Exercises

    4) What happens if you delete the line with "chomp"?
    5) Write a program that asks two people for their names; stores the names in variables called $name1 and $name2; says hello to both of them.

    3 Operators for Numbers

    $a = 3 -4 +10;
    $b = 5*6;
    $c = 7/8;
    print "These are the values: $a $b $c \n";
    print "Increment $a by one: ";
    print $a;
    print "\n";
    print "Decrease $a by one: ";
    print $a;
    print "\n";

    3.1 Exercises

    6) Execute the script. Make sure you understand every line.
    7) Write a script that asks a user for a number. The script adds 3 to that number. Then multiplies the result by 2, subtracts 4, subtracts twice the original number, adds 3, then prints the result.

    3.2 Example

    #!/usr/local/bin/perl -w
    # This program converts from US $ to Canadian $
    print "Money value in US \$ ";
    $us_money = <STDIN> ;
    chomp $us_money;
    $can_money = $us_money /0.6;
    print "US\$ $us_money = Canadian \$ $can_money\n";

    3.3 Exercises

    8) In analogy to the example, write a script that asks users for the temperature in F and prints the temperature in C. (Conversion: Celsius = (F - 32) * 5/9 )

    4 Strings

    A string is delimited by double quotes (""). Certain special characters can be used, such as "\n" and "\t". Variables are interpreted, i.e. 'print "$name"' prints the value of '$name' and not $-sign followed by 'name'. To print the characters $, ", \, @, they must be preceded by a backslash (\).

    print "hello\n";
    print "hello\\n";
    print "\$5.00\n";
    print "She said: \"hello\"\n";
    print "\tThis is indented\n";
    $a = "apples"; $b = "pears";
    print "$a and $b\n";

    4.1 Exercises

    9) Write Perl print statements for the following text (with the same linebreaks, etc):

    Snoopy bought a CD called "Greatest Hits" on the WWW for
    $10.00. To buy the CD he had to send an email message to This is what the design on the CD
    cover looked like:

           \  |  /
             @ @

    4.2 Operators and functions for strings

    chop $a; # removes the last character
    chomp $a; # removes the last character if it is a newline character
    $a = $b . $c; # concatenate $b and $c
    $a = $b x $c; # $b repeated $c times

    4.3 Example

    #!/usr/local/bin/perl -w
    # program that demonstrates operating with strings
    print "Please, type your favorite color: ";
    $color= <STDIN>;
    chomp $color;
    $color = $color . "***";
    chop $color; chop $color;
    $color = $color . "!";
    $color = $color x 5;
    print "$color\n";

    (If you are unsure what this program does, add 'print "$color\n";' after every line so that you can see how the content of the variable is changed at each step.)

    4.4 Exercises

    10) Write a program that asks users for their favorite color. Create the following output (assuming "red" is the chosen color).
    red red red red red red red red red red  
    red                                 red
    red                                 red
    red red red red red red red red red red
    Hints: For the first and last lines: concatenate the string with "." and use the x-operator. For the second and third line use "\t". Don't worry about the length of different color words. It is not necessary to draw the square exactly.