Welcome Mark.Allan,

If you loop on the file as:

   my $string = "";
   while ( <$IN> )                    ## $IN needs to be open
   {   chomp;
       if ( $_ eq "END" )
       {   $string = join ( " ", split " ", $string );
           # $string =~ s/$other//g;   ## In case you need to remove o
+ther characters
           print $OUT "$string\n";    ## $OUT is open output file
           $string = ""; next;
       }
       $string .= $_;
   }
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I know you didn't want code, but it was easier to type code then describe :-)

That special use of 'join' is in the Camel book (3rd edition) on page 154. It removes whitespace before and after the string, plus reduces multiple spaces to 1. I typed this in, so there may be some typos, but it should get you going, and remember to use 'use strict; use warning;' in your code.

Hope it helps.