you can pretty much treat a file handle as a list of lines. Any old loop structure will do. I'm partial to foreach. The following code prints the first six lines of a file.

open(FILE,'<some_file.txt'); 
for((<FILE>)[0..5]){
    print;
}
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Now lets say your special delimiter is a weird tie fighter thing like this :o:
We can slurp every line up to and including that like so.

open(FILE,'<some_file.txt') or die("cant open file: $!"); 
my $data;
for(<FILE>){ 
   if($_ !~ /:o:/){
       $data .= $_;
   }else{
       $data .= $_;
       last;
   }
}
close FILE;
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Of course we should also check the first however many lines for the special character first to avoid slurping up the entire file if we dont find that character.