#! /usr/bin/env perl

   $key = "c";
   $select = 1;

#  Read switches.
   while ( $_ = $ARGV[0], /^-/ ) {
      shift;
      last if /^--$/;
      if ( /^-f/ ) { $key = "f" };
   }

#  Read input lines.
   line: while (<>) {

#  Detect start of prologue and initialise prologue text.
      if ( /^[fc]\+ *$/ ) {
         $select = 0;
         if ( /^$key\+ *$/o ) { $select = 1; }
         next line;
      }

#  Detect end of prologue.
      if ( /^[fc]- *$/ ) { $select = 1; next line }

#  Process the prologue contents.
      if ( $select ) { print; }

   }