foreach (@dat)
  {
    s/number/NEWWORD/;
    print DATA $_;
  }
  close(DATA);   

##</code><code>##

  perl -pi.bak -e 's/number/NEWWORD/;' file.txt

##</code><code>##

foreach (@dat)
  {
    s/number/NEWWORD/;
    print DATA $_;
  }
  close(DATA);