!/usr/bin/perl

open (FH, 'F:\\perl\about BUCT.txt ') || die $!;
open (OUT,'>>','F:/perl/wordlist.txt')or die $!;
sub byDescendingValues{
 $value= $freq{$b}<=>$freq{$a};
if ($value==0){
return $a cmp $b;
}else{
return $value;
}
}

while(<FH>) {
   {$line=$_ ;
        chomp $line;
        @words = split (/[\.\?,!;:]+\s+/, $line);}

        foreach $x (@words) {
              ++ $wordfreq{$x};
              }
              }
        close FH;

          foreach $x(sort byDescendingValues keys %freq){

   print OUT "$x,$wordfreq{$x}\n";
   }

是这里有问题吧，'F:\\perl\about BUCT.txt '，反斜杠在单引号中应该写成双的 \\ ,否则不按路径执行。