use v5.18;
use warnings;
use autodie;


my @replace = (qw/vss vdd/);

open(my $in,'<','input.txt');
my @lines = <$in>;
close $in;

LOOP:
for my $word (@replace) {
  my $start = -1;
  for my $i (0..$#lines) {
    if ($start == -1) {
      next unless $lines[$i] =~ /Power\s+information\s+for\s+$word\s+/;
      $start = $i;
    } else {
      next unless $lines[$i] =~ /}/;
      splice @lines,$start,$i - $start + 1;
      redo LOOP;
    }
  }
}
say @lines;

# save @lines to temporary file name
# rename input.txt to backup.txt
# rename temporary file to input.txt