Something like this perhaps (untested)

open(IN, 'in.txt') or die "Can't open input file: $!\n";
open(OUT, '>out.txt') or die "Can't open output file: $!\n";

while (<IN>) {
  my ($stuff, $dregs) = split m[ // ];
  print OUT reverse($stuff), "\n";
}
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European Perl Conference - Sept 22/24 2000, ICA, London
<http://www.yapc.org/Europe/>