You can use hash like so:

use warnings;
use strict;
use Data::Dumper;

my %property_para;

open my $fh, '<', "temp.txt" or die "can't open file: $!";
while ( defined( my $line = <$fh> ) ) {
    chomp $line;
    my ( $property, $value ) = split /=/, $line;
    $property_para{$property} = $value;
}
close $fh or die "can't close: $!";

open $fh, '<', "current.txt" or die "can't open file: $!";
while ( defined( my $line = <$fh> ) ) {
    chomp $line;
    my ( $property, $value ) = split /=/, $line;
    $property_para{$property} = $value if exists $property_para{$prope
+rty};
}
close $fh or die "can't close: $!";

$Data::Dumper::Varname = 'ADDRESS';
print Dumper \%property_para;

# OR

my %property_name;

open_do_work( 'temp.txt', sub { $property_name{ $_[0] } = $_[1] } );
open_do_work( 'current.txt',
    sub { $property_name{ $_[0] } = $_[1] if $property_name{ $_[0] } }
+ );

$Data::Dumper::Varname = 'ADDRESS';
print Dumper \%property_name;

sub open_do_work {
    my ( $file, $coderef ) = @_;
    open my $fh, '<', $file or die "can't open : $!";
    while ( defined( my $line = <$fh> ) ) {
        chomp $line;
        my ( $property, $value ) = split /=/, $line;
        $coderef->( $property, $value );
    }
}
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