while (my $line = <$input_file>) { 
     chomp $line; 
     next unless $line =~ /City\s*$/; # discards lines which are not cities 
     my @temp_array = split /\s*:/; # split the line into an array 
     my $city = shift @temp-array; # get the city name 
      # now try to find duplicates 
}

use strict; 
use warnings; 
my %seen; 
while (<DATA>) { 
    my ($name, $type) = split /\s*:\s*/; 
    $type =~ s/\s*$//; 
    next if $type ne 'City' or $seen{$name}++; 
    print;  
} 
__DATA__ 
Bengaluru : City  
Maharastra : State  
Tamil Nadu : State  
Mumbai : City  
Chennai : City  
Karnataka : State  
Bengaluru : City  
Hyderabad : City  
Bengaluru : City

Bengaluru : City  
Mumbai : City  
Chennai : City  
Hyderabad : City