perl function

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# code : Array
@book=("PHP","Perl");
@morebook=("database","internet");
@morebook=("database","internet",@book);
# Output: @morebook=("database","internet","PHP","Perl");

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# Code: scalar(@arr)
# This function forces an array or hash to be interpreted as a scalar.
# This is useful to find out the number of elements in an array or hash.
# Use this function to find out the size of an array or hash, 
# preparatory to iterating over it in a loop and processing its contents.
# define array
@data = ('apple', 'peach', 'banana');
# get size
print "The array has " . scalar(@data) . " elements";
# Output: The array has 3 elements


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# Code: exists $hash{$key}
# This function can be used to test if a particular key exists in a hash.
# define hash
%data = ('king' => 'queen', 'prince' => 'princess');
# check if key exists
if (exists $data{'king'}) {
  print "Found!";
}
# Output: Found!


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# Code: push(@arr, $val)
# push จะเพิ่มค่าตัวแปรให้กับตัวแปรตัวสุดท้าย
# define array
@data = ('a', 'b', 'c');
# add element
push(@data, 'd');
print "@data ";
# Output: a b c d


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# Code: pop(@arr)
# define array
@data = ('a', 'b', 'c');
# add element
pop(@data);
print "@data ";
# Output: a b


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# Code: unshift(@arr, $val)
# This function adds a new element to the beginning of an array.
# define array
@data = ('a', 'b', 'c');
# add element
unshift(@data, 'z');
print "@data ";
# Output: z a b c


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# Code: shift(@arr)
# This function removes an element from the beginning of the array.
# define array
@data = ('a', 'b', 'c');
# remove element
shift(@data);
print "@data ";
# Output: b c


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# Code: splice(@arr, $offset, $length, @arr2)
# This function removes a segment of an array, starting from the element at position $offset 
# and continuing until $length elements have been removed. If the optional @arr2 argument is present,
# the extracted segment is replaced with the element of array @arr2.
# Use this function to extract subsets of an array, or to replace elements in an array with new values.
# define array
@data = ('king', 'queen', 'knight', 'bishop');
# remove middle elements
splice(@data, 1, 2);
print "@data ";
# Output: king bishop


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# Code: delete $hash{$key}
# This function deletes a key from a hash, together with its associated value.
# Use this function to remove elements from a hash. 
# define hash
%data = ('king' => 'queen', 'prince' => 'princess');
# remove element with key 'king'
delete $data{'king'};


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# Code: split($delim, $str)
# This function decomposes a string by splitting it on delimited $delim and returns the individual 
# components as elements of a numerically-indexed array. These elements can then be processed in a loop.
# Use this function to split comma-delimited lists into independent array elements.
# define string
$str = "cat,hog,dog,log";
# split string on comma delimiter
@words = split(",", $str);
foreach $w (@words) {
  print "$w\n";
}
#Output:
#cat
#hog
#dog
#log


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# Code: join($sep, @arr)
# This function joins the various elements of an array into a single string, 
# using the value of $sep to separate them from each other.
# Use this function to create a single string from multiple independent array elements,
# using spaces, commas or other separators to glue them together.
# define array
@data = ("Harry", "Joan", "Tom");
# create string from array
print join(" and ", @data) . " are friends";
# Output: Harry and Joan and Tom are friends


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# Code: keys(%hash)
# This function returns the keys of a hash as a numerically-indexed array. 
# The function is the counterpart of the values() function, discussed next.
# Use this function to extract the keys of a hash into a separate data structure for further processing.
# define hash
%data = ('a' => 'apple', 'b' => 'bat', 'c' => 'cat');
# get and print hash keys
@keys = keys(%data);
print "@keys\n";
# Output: c a b


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# Code: values(%hash)
# This function returns the values of a hash as a numerically-indexed array.
# The function is the counterpart of the keys() function, discussed previously.
# Use this function to extract the values of a hash into a separate data structure for further processing.
# define hash
%data = ('a' => 'apple', 'b' => 'bat', 'c' => 'cat');
# get and print hash keys
@vals = values(%data);
foreach $v (@vals) {
  print "$v ";
}
# Output: cat apple bat


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# Code: reverse(@arr)
# This function reverses the order of elements of an array, placing the last element first and vice-versa.
# Use this function to re-sort an array's elements in the opposite direction to their current sort.
# define array
@data = ('apple', 'peach', 'banana');
# reverse array
@rev = reverse(@data);
print "@rev ";
# Output: banana peach apple


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# Code: sort(@arr)
# This function can be used to sort the elements of an array or hash. By default,
# this function sorts using standard string comparison rules; however,
# you can override this by passing it the name of a custom sorting subroutine.
# Use this function to reset the internal order of elements of an array,
# or to arrange elements alphabetically, numerically or in a custom order.
# define hash
@data = ('oranges', 'peaches', 'grapes', 'apples', 'lemons');
# sort alphabetically
@sorted = sort(@data);
print "@sorted ";
# Output: apples grapes lemons oranges peaches


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# Code: foreach
@myNames = ('Larry', 'Curly', 'Moe');
foreach (@myNames) {
  print $_;
}
# Output: LarryCurlyMoe


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# Code: foreach
@myNames = ('Larry', 'Curly', 'Moe');
foreach $name (@myNames) {
  print $name;
}
# Output: LarryCurlyMoe


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# Code: qw
# quote word in Perl
@myNames1 = ('Jacob', 'Michael', 'Joshua', 'Matthew', 'Alexander', 'Andrew');
@myNames2 = qw(Jacob Michael Joshua Matthew Alexander Andrew);
@myNames3 = qw/Jacob Michael Joshua Matthew Alexander Andrew/;
print "\@myNames1 = @myNames1\n";
print "\@myNames2 = @myNames2\n";
print "\@myNames3 = @myNames3\n";
# Output: 
# @myNames1 = Jacob Michael Joshua Matthew Alexander Andrew
# @myNames2 = Jacob Michael Joshua Matthew Alexander Andrew
# @myNames3 = Jacob Michael Joshua Matthew Alexander Andrew


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# Code: Single and Double Quoted Strings
$my_name = 'Bobby';
print "$my_name\n";
print '$my_name\n';
# Output: 
# Bobby
# $my_name\n