Section 1
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What does my $ar = [1..5]; mean?
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Mar 1, 2020
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Section 1
(50 cards)
What does my $ar = [1..5]; mean?
It means $ar is an anonymous array reference to an array containing 1,2,3,4,5. To create an anonymous array reference, use square brackets [ ] instead of parentheses ( ).
What is the dereference?
What is the "for of" equivalence in Perl?
for my $array_element ($the_array){ say $array_element; } OR foreach my $array_element ($the_array){ say $array_element; } OR for (@the_array){ say "Your place in line is $_"; } //here $_ is used when no variable is declared
What does 'my' do?
A 'my' keyword declares the listed variables to be local (lexically) to the enclosing block, file, or eval. That variable would now be available to the scope of that file. If more than one variable is listed, the list must be placed in parentheses.
What is @ARGV?
the arguments to the command line of the program eg. $ perl examples/shift_argv.pl one two 'one' and 'two' are @ARGV
What's the difference between a pragma and a module?
How do you map all elements in an array?
my @mapped = map{$_ * 2} @number_arr;
How do you sort or reverse sort an array?
sort @arr; reverse sort @arr;
What is the convention for naming the constructor in Perl?
sub new
How do you add a break statement?
By typing "last;"
How do you check if a key exists in a hash?
exists $dogs{ChiChi};
What does 'use vars qw($VERSION)' do?
It creates a global variable named $VERSION. Note that use vars has been superseded by our. With perl5.6 you can use the 'our' operator instead
How do you filter out values in array?
By using grep, eg. my @large_numbers = grep{ $_ > 100 } @some_num_arr;
How do you make an array out of some elements in another array?
my @larger_arr = (1,2,3,4,5,6); my @smaller_arr = @larger_arr[3, 5]; so now @smaller_arr = (4, 6);
What is a scalar?
A data type that holds one variable, one value A dollar sign $ makes a variable a scalar
How do you split a string?
my $str_to_be_splitted = "Split,me,please"; my @splitted = split /,/ , $str_to_be_splitted; What you put between the // will be what the string will be splitted by
How do you make an array of keys from a hash?
my @arr_of_keys = keys %target_hash;
How do you uppercase or lowercase all letters in a string?
uc $string lc $string
What is a pragma?
A pragma is a module which influences some aspect of the compile time or run time behaviour of Perl, such as strict or warnings
What are modules named?
.pm instead of .pl
How do you round a number?
int(number_to_be_rounded);
How do you delete a key value pair in a hash?
delete $dogs{Lucky};
What are class, object, method, and constructor called in Perl?
A class is a package. An object is a reference that knows its class. A method is a subroutine. A subroutine called new() is used to construct the object
How do you splice an array?
splice @arr, 0, 3; 0 is the starting spliced index; 3 is the number of items you want to splice; You can't store the spliced values into a separate array
How do you add a new key-value pair to a hash?
$some_hash{newKey} = "new value";
What are Misc::HTML and Misc::Utility?
How do you use pass in an array or a hash properly into a function?
You need the \ thing in front of the array or hash when you pass them in as arguments eg. printTest(\@sample_Array); within the the function definition, you need to reference to the array with the $ sign eg. @$sample_Array
What is IO::File module used for?
For reading and writing files
What does 'use' do?
This function imports all the functions exported by MODULE, or only those referred to by LIST, into the name space of the current package Note that a use statement is evaluated at compile time. A require statement is evaluated at execution time.
What does @{} mean?
dereference
What is the meaning of @_?
@_ is the list of incoming parameters to a subroutine (ie. function). It's an array of parameters. Usually, you expand the parameters passed to a sub using the @_ variable: sub generateNames{ my ($a, $b, $c) = @_; ... } # call the test sub with the parameters generateNames('alice', 'bob', 'charlie');
How do you switch values of 2 scalars?
($first, $second) = ($second, $first);
How do you join array elements>
join(", ", $the_array)
How can you get the count of elements in an array?
Assign the array to a scalar eg. my @testArr = (1,2,3,4); my $count = @testArr; $count would print out 4 OR my $count = scalar @testArr;
What is the difference between print and say?
Say automatically adds a new line
Print doesn't. To add a new in print, you need to add the new line character
How do you reverse an array?
reverse @arr;
What is $_ ?
It's a global variable that happens to be used by default by many operators. It is used when no variable is declared. In Perl, several functions and operators use this variable as a default, in case no parameter is explicitly used.
Can you use single quote in Perl?
Yes, but it would not recognize variable embedded in it. For that, you need double quote
How do you generate a random number from between 1 to 10?
rand 11;
How do you make a variable retain its value after a function is called?
by using state eg. state $kept_value = 0;
How do you make a range of numbers or letters array?
my @letters = ('a' .. 'z'); //this would make an array of letters from a to z my @numbers = (1 .. 10); //this would make an array of numbers of 1 to 10
How do you set a default parameter in case no parameter was passed?
sub say_hello { my ($name) = @_; $name ||= "Anonymous"; return "Hello $name"; }
What is Perl reference used for?
What does shift do?
If used in the main program, it will shift (remove and return) the first value from @ARGV, the argument list of your program. If used inside a subroutine, it will shift the first value from @_, the argument list of the sub. 'shift' accepts an array and extracts the first element (actually removing it from the array). If you don't provide any array, it uses @ARGV (the arguments to the command line of the program) to read the data. If you're inside a function, it uses @_, namely, the parameters of the function. In all cases, shift removes the element at list index 0 and returns it, shifting all remaining elements down one. Inside a sub, shift without an argument (bare shift) operates on the @_ list of subroutine parameters. Suppose I call mysub('me', '22') sub mysub { my $self = shift; # return $_[0], moves everything else down, $self = 'me', @_ = ( '22' ) my $arg1 = shift; # returns $_[0], moves everything down, $arg1 = '22', @_ = () } If you call a method on an object like this: $obj->my_method('one'); Then the my_method subroutine will actually be passed two arguments in @_. The first is the object that the method was invoked on (sometimes called the invocant) which in this example is $obj. Whenever you call the new() method, Perl automatically passes the class name (eg. Animals) as the first argument to the special array @_. The second argument will be the string 'one'. It is very common in object-oriented code to start a method definition like this: sub my_method { my $self = shift; } Which means $self will now contain the invocant (the class/object that invoked the function) and @_ will be left with all the remaining arguments.
What does the 'sub' keyword do?
Define a function. In some languages there is a distinction between functions and subroutines. In Perl there is only one thing. It is created with the sub keyword, and it always returns a value. Perl programmers often use the two words function and subroutine interchangeably.
How do you add double quote to a string in Perl?
"My name is \"$variable_name\"" OR a cleaner way of writing is qq{The book I'm reading is called "$book_title"}
What is @INC?
@INC is a built-in array perl provides. It contains a series of directories, the "search path" for perl when trying to load a module. When perl encounters a use statement, a require statement, or a do statement: use Module::Name; require Module::Name; do "Module/Name.pm"; perl will go over the directories listed in @INC and check if the appropriate file can be found. In our example, if we try to load Module::Name. Perl will check if there is a Module subdirectory in any of of the directories with a file called Name.pm in the directory. perl will load the first such file.
How can you determine whether a Perl module named Foo is available for you to use?
perl -e 'use Foo;'
How do you dereference a hash?
my %dogs = ( "Cookie"=>"fat", "Minnie"=>"shy", "Maggie"=>"overly affectionate", "Lily"=>"old and cute" ); To get the word "fat", we do $dogs{Cookie} Notice that %dogs is now $dogs
Can you increment letter in Perl?
Yes eg. my $a = "a"; my $b = ++$a; say $b; //this would print out "b"
Section 2
(8 cards)