use CGI qw(:standard append add_parameter);
use strict ;
use warnings ;

print CGI::header() ;

my $out ;

{ local *STDOUT ;
  local *STDERR ;
  open (STDOUT,">>", \$out) ;
  open (STDERR,">>", \$out) ;
  select STDOUT; $| = 1;  # make unbuffered
  select STDERR; $| = 1;  # make unbuffered
  print "message1\n" ;
  warn "error1\n";
  print "message2\n" ;
}
print "Result: $out\n";