一个一个字符处理字符串

一个一个字符处理字符串

1.split函数

   %seen = ( );
   $string = "an apple a day";
   foreach $char (split //, $string) {
       $seen{$char}++;
   }

2./(.)/g 但是(.)永远不会是newline
   %seen = ( );
   $string = "an apple a day";
   while ($string =~ /(.)/g) {
       $seen{$1}++;
   }

3.unpack("C*")也可以逐个处理字符:(这个例子是累加字符串里每个字符ascii码的累加值)
   $sum = 0;
   foreach $byteval (unpack("C*", $string)) {
       $sum += $byteval;
   }
   print "sum is $sum\n";
   # prints "1248" if $string was "an apple a day"

$sum = unpack("%32C*", $string); #这个方法比上面更快,这个返回32位的checksum值.

4 .<>是默认的输入流,其实就是ARGV.
     这个模拟sysv的checksum程序:

   #!/usr/bin/perl
   # sum - compute 16-bit checksum of all input files
   $checksum = 0;
   while (<>) { $checksum += unpack("%16C*", $_) }
   $checksum %= (2 ** 16) - 1;
   print "$checksum\n";
   
   Here's an example of its use:
   % perl sum /etc/termcap
   1510

   If you have the GNU version of sum, you'll need to call it with the —sysv option to get the same answer on the same file.
   % sum --sysv /etc/termcap
   1510 851 /etc/termcap
一个详细的例子：



 #!/usr/bin/perl
  # slowcat - emulate a   s l o w   line printer
  # usage: slowcat [-DELAY] [files ...]
  $DELAY = ($ARGV[0] =~ /^-([.\d]+)/) ? (shift, $1) : 1; #这里[.]取消了.的特殊性。使其为一般意义。shift移除了@ARGV第一个变量和长度减一。
  $| = 1; #不为0就强行清空输出或打印。
  while (<>) {  #<>为@ARGV指定的文件句柄
      for (split(//)) {
          print;
          select(undef,undef,undef, 0.005 * $DELAY);  #select函数设置屏幕输出。这里是设置延迟。
      }
  }