my $file = "file"; # why not...
my $temp = "temp"; # makes sense if you later want to use
                   # some other basename for your sequence of files

foreach (1..5){
  open $file, '>', "$temp$_"; # you just turned $file from a string into a filehandle...
  ...
}
##</code><code>##

foreach (@lines) {
  $_ = uc; # ALL CAPS WOOOOOO
  s/$/!!!/; # EVERY LINE IS AN EXCLAMATION!!!
  print;
}

##</code><code>##

my @timesTable;
foreach my $row (0..12) { #
  foreach my $col (0..12) {
    @timesTable[$row][$col] = $row * $col;
  }
}

##</code><code>##

for ($leetString) { # "loops" only once
  s/very/uber/g;
  tr/astloe/457103/;
  s!w!\\/\\/!g;
}