Unbalanced `if-else` Blocks

        sub each_file {
          return unless  -T $_ ;

          print "processing $File::Find::name\n";
          unless ( open F, "< $_" ) {
            print "Error opening file for read: $!\n";
            return;
          }

          my $s = <F>; 
          close F;
          unless ( open F, "> $_" ) { 
            print "Error opening file for write: $!\n";
            return;
          }

          $s =~ s/COLUMN1/COLUMN1/ig;
          print F $s;                
          close F;
        }

The flow is now simple and linear
It's obvious what the error-handling blocks are doing
They can all be understood independently
Symmetry between reading and writing becomes clearer

Unbalanced if-else Blocks

Unbalanced `if-else` Blocks