perl分组捕获

问题如下 ：

http://zhidao.baidu.com/question/501928970.html?push=keyword

?

解决如下：

#! /usr/bin/perl -w

use strict;
my $string = "abc r=3 def r=3 test r=3 over";
print $string,"n";

$string =~ s/(?<=def r=)d/5/;  #?<=  	匹配exp后面的位置
print $string,"n";


$string = "abc r=3 def r=3 test r=3 over";  #?=  匹配exp前面的位置
$string =~ s/d(?= def)/5/;
print $string,"n";


$string = "abc r=3 def r=3 test r=3 over";  #?!  匹配后面跟的不是exp的位置
$string =~ s/d(?! def)/5/;
print $string,"n";

$string = "abc r=3 def r=3 test r=3 over";  #?<!  匹配前面不是exp的位置
$string =~ s/d(?<! def)/5/;
print $string,"n";