Perl | List Functions

A list in Perl is a collection of scalar values. We can access the elements of a list using indexes. Index starts with 0 (0th index refers to the first element of the list). We use parenthesis and comma operators to construct a list. In Perl, scalar variables start with a $ symbol whereas list variables start with @ symbol.
List provides various pre-defined Functions to perform operations with ease. Some of these Functions are as below:

• join() function
  join() function is used to combine the elements of a List into a single string with the use of a separator provided to separate each element. This function returns the joined string. A separator can work only between the pairs. A separator can’t be placed at either end of the string. In order to join the strings without a separator, an empty parameter is passed to the function.

  Syntax: join(Separator, List)

  Parameter:

  • Separator: provided to separate each element while joining
  • List: to be converted to single String

  Returns: a joined String

  Example :

  #!/usr/bin/perl
  
  # Initializing list with alphabets A to Z
  @list = (A..Z);
  
  # Printing the original list
  print "List: @list\n";
  
  # Using join function introducing
  # hyphen between each alphabets
  print "\nString after join operation:\n";
  print join("-", @list);

  Output:

  List: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
  
  String after join operation:
  A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z
  

• reverse() function
  Reverse() function in Perl returns the elements of List in reverse order in a list context. While in a scalar context, it returns a concatenated string of the values of List, with all characters in opposite order. It returns String in Scalar Context and List in List Context.

  Syntax: reverse List

  Parameter:
  List: list to be reversed

  Returns: elements in reverse order

  Example:

  # Initializing a list
  @list = ("Raj", "E123", 12000);
  
  # Reversing the list
  @rname = reverse(@list);
  
  # Printing the reversed list
  print "Reversed list is @rname";
  
  # Initializing a scalar
  $string = "GeeksforGeeks";
  
  # Reversing a scalar
  $r = reverse($string);
  print "\nReversed string is $r";

  Output:

  Reversed list is 12000 E123 Raj
  Reversed string is skeeGrofskeeG
  

• map() function
  map() function in Perl evaluates the operator provided as a parameter for each element of List. For each iteration, $_ holds the value of the current element, which can also be assigned to allow the value of the element to be updated. map() function runs an expression on each element of an array and returns a new array with the updated results. It returns the total number of elements generated in scalar context and list of values in list context.

  Syntax: map(operation, List)
  Parameter:

  • operation: to be performed on list elements
  • List: whose elements need to be changed

  Example :

  # Initializing a list
  @Dept = ('comp', 'inft', 'extc', 'mech');
  
  # Converting first character capital
  @upd1 = map(ucfirst, @Dept);
  
  # Printing list
  print "List with First char capital: ";
  foreach $i (@upd1)
  {
     print "$i, ";
  }
  
  # Converting all characters capital
  @upd2 = map(uc, @Dept);
  
  # Printing list
  print "\nList with all char capital: ";
  foreach $i (@upd2)
  {
     print "$i, ";
  }

  Output:

  List with First char capital: Comp, Inft, Extc, Mech, 
  List with all char capital: COMP, INFT, EXTC, MECH, 

• sort() function
  sort() function in Perl is used to arrange the List according to the condition of sorting specified to the function. If no condition is specified, then it sorts according to normal alphabetical sequence.
  If a condition is specified then the function sorts the List according to the condition.

  Syntax: sort(condition, List)

  Example

  # Initializing two lists
  @country = ('India', 'Qatar', 'Bangladesh', 'France', 'Italy');
  @capital = ('Delhi', 'Lahore', 'Dhaka', 'Paris', 'Rome');
  
  # Printing countries in sorted order
  print"Countries in sorted order: \n";
  print sort @country;
  print "\n";
  
  # Printing sorted country and capital values
  print "\nCombining both the lists in sorted order:\n";
  print sort @country, @capital;
  print "\n";
  
  # Initializing a list with number
  @list = (19, 4, 54, 33, 99, 2);
  
  # Sorting in descending order
  @s = sort{$b <=> $a} @list;
  print "\nPrinting numbers in sorted order:\n";
  foreach $i(@s)
  {
      print "$i, ";
  }

  Output:

  Countries in sorted order: 
  BangladeshFranceIndiaItalyQatar
  
  Combining both the lists in sorted order:
  BangladeshDelhiDhakaFranceIndiaItalyLahoreParisQatarRome
  
  Printing numbers in sorted order:
  99, 54, 33, 19, 4, 2,