V1=/home/user
V2=$V1/test
V3=$V2/file.txt

##</code><code>##

Read variables
open my $vars, '<:utf8', "$Bin/vars.txt" or die $! ;

while (<$vars>) {

chomp;

my ($key, $value) = split(/=/, $_);
     $vars{$key} = $value;
	
}

my $V1 = $vars{'V1'};
my $V2 = $vars{'V2'};
my $V3 = $vars{'V3'};

print "$V1\n";
print "$V2\n";
print "$V3\n";

close ($vars);

##</code><code>##

/home/user
/$V1/test
/$V2/file.txt

##</code><code>##

/home/user
/home/user/test
/home/user/test/file.txt