my $KPI0=10;
my $KPI1=20;
my $KPI2=30;
my $KPI3=40;
my $KPI4=50;

      for($i=0;$i<5;$i++){
        my $var="$KPI$i";
        print "line"."$var"."\n";
      }

my expected output is  
line10
line20
line30
line40
line50