while(<$fh>){
    if(/START/ .. /ENDE/){
        push(@lines,$_);

while(defined (my $line = <$fh>)){
   if($line =~ /START/ .. $line =~ /ENDE/){
       push(@lines,$line);

while ( <$fh> ) { push @lines, $_ if /START/ .. /END/ }

my @lines = grep { /START/ .. /END/ } <$fh>;

my @lines;
open my $fh,'<',$file or die $!;
while(<$fh>){
   if(/START/ .. /ENDE/){
       foo();
       push(@lines,$_);
   }
}
close $fh;

print $_ for @lines;

sub foo {
   open my $fh, '<',$otherfile or die $!;
   while (<$fh>) {
      # operations
   }
   close $fh;
}

while(defined (my $line = <$fh>)){

while(defined (my $line = <$fh>)){

perl -MO=Deparse -wle'
while (my $line = <>) {
print $line
}'
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
while (defined(my $line = <ARGV>)) {
    print $line;
}
-e syntax OK

while ( <DATA> ) { /START/ .. /END/ or push @lines, $_ }