#open file, read only
open(DATA, "<filename.txt");

open(SUBJECT, ">subject.txt");
open(COMMENT, ">comment.txt");
open(LENGTH, ">length.txt");

my $filetoprint = "";

#start a run through the file
while(<DATA>)
{
 #grab next line
 my $line = $_;
 # trim line breaks from $line and return it to the variable
 chomp($line);

 # Check start of line
 if ($line =~ m/^SUBJECT(.+)/)
 {
  # set variable indicator to Subject
  $filetoprint = "Subject";
  # remove first word from $line by passing the matched portion back into it
  $line "$1";
 }

 # Check start of line
 if ($line =~ m/^LENGTH(.+)/)
 {
  # set variable indicator to Length
  $filetoprint = "Length";
  # remove first word from $line by passing the matched portion back into it
  $line "$1";
 }


 # Check start of line
 if ($line =~ m/^COMMENT(.+)/)
 {
  # set variable indicator to Comment
  $filetoprint = "Comment";
  # remove first word from $line by passing the matched portion back into it
  $line "$1";
 }

# if there has been a previous match (this line or any following print out to the appropriate file
 if ($filetoprint eq "Subject") {print SUBJECT "$line\n";}
 if ($filetoprint eq "Comment") {print COMMENT "$line\n";}
 if ($filetoprint eq "Length")  {print LENGTH  "$line\n";}

}

close SUBJECT;
close COMMENT;
close LENGTH ;

if ($filetoprint eq detail)
{
 #print the detail content to the detail element of the current hash in the array
 $arrayofhashes[$i]->[detail] = "${$arrayofhashes[$i]->[detail]}$line\n";
}
etc