use strict;

my $in_section = 0;

foreach (<>) {
  $in_section=1, next if m{if\s+\(some\s+condition2\s+=\s+0\)}; 
  $in_section=0, next if m{^\s*end\s+if;}; # next could be omitted...here
  print if $in_section;
}

__END__
read this data 3;
read data 4;
read this data 6;