if ( ..A... ) {
   if ( ..B.. ) {
       if ( ..C.. ) {
           if ( ..D.. ) {
               print .....
           } else {
               print ...
           }
        } else {
           if ( .. D2.. ) {

... you get the idea ...

##</code><code>##

my $flag1 = cond1;
my $prefix = (( cond2 ) ? "strting1" : "strring2";
...
print "$prefixA$suffixB" if ( condC );