if ($choice eq 'a'){
    ...
  }

##</code><code>##

if (CONDITION1) {
    ...
}
if (CONDITION2) {
    ...
}

##</code><code>##

if (CONDITION1) {
    ...
    if (CONDITION2) {
        ...
    }
}

##</code><code>##

if (CONDITION1) {
    ...
}
elsif (CONDITION2) {
    ...
}
elsif (CONDITION3) {
    ...
}
else {
    ...
}

##</code><code>##

$ perl -E 'my @x = qw{Jeff JEFF jEfF}; say lc $_ for @x'
jeff
jeff
jeff

##</code><code>##

$ perl -E 'my @x = qw{Jeff JEFF jEfF}; say ucfirst lc $_ for @x'
Jeff
Jeff
Jeff

##</code><code>##

$ perl -E 'my @x = qw{Jeff JEFF jEfF}; say ucfirst $_ for @x'
Jeff
JEFF
JEfF

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

{
    my %father_of = get_son_to_father_map();

    display_menu();

    while (1) { 
        my $menu_selection = get_menu_selection();

        if ($menu_selection eq 'e') {
            print "Exiting ...\n";
            last;
        }
        elsif ($menu_selection eq 'a') {
            print "Son-father pair addition.\n";

            print "Enter son's name: ";
            chomp( my $son = ucfirst lc <STDIN> );

            if (exists $father_of{$son}) {
                print "$father_of{$son} is the father of $son\n";
            }
            else {
                print "Enter father's name: ";
                chomp( my $father = ucfirst lc <STDIN> );
                $father_of{$son} = $father;
                
            }
        }
        else {
            print "Invalid menu selection! Try agin.\n";
        } 
    }

    print "Done!\n";
}

sub display_menu {
    print <<'MENU';

    Menu Selections
    ===============

    a - add son-father pair
    e - exit
MENU

    return;
}

sub get_menu_selection {
    print "\nEnter menu selection: ";
    chomp( my $selection = lc <STDIN> );
    return $selection;
}

sub get_son_to_father_map {
    return (
        Jeff   => 'Doug',
        Thomas => 'Evan',
        Robert => 'Jason',
        Bruce  => 'Richard',
        Clark  => 'Jon',
    );
}

##</code><code>##


    Menu Selections
    ===============

    a - add son-father pair
    e - exit

Enter menu selection: qwerty
Invalid menu selection! Try agin.

Enter menu selection: 
Invalid menu selection! Try agin.

Enter menu selection: a
Son-father pair addition.
Enter son's name: JEFF
Doug is the father of Jeff

Enter menu selection: a
Son-father pair addition.
Enter son's name: bRuCe
Richard is the father of Bruce

Enter menu selection: a
Son-father pair addition.
Enter son's name: fred
Enter father's name: BILL

Enter menu selection: a
Son-father pair addition.
Enter son's name: FrEd
Bill is the father of Fred

Enter menu selection: e
Exiting ...
Done!