perl中的$_ $1、$2怎么识别

jinger18

open(F,">$dir/duxiu_cookie");
                if($cookies=~/(AID_dsr=.*?);/){print F "$1\n";}
                if($cookies=~/(userid_dsr=.*?);/){print F "$1\n";}
                if($cookies=~/(userName_dsr=.*?);/){print F "$1\n";}
                if($cookies=~/(enc_dsr=.*?);/){print F "$1\n";}
                close(F);
和
                                 my $yrno=0,$yrstart=-1,$yrend=-1;
                         while($request =~ s/(AND|OR|NOT)*\s*WYR = \(\s*(.*?)\s*\)//){
                $yr=$2;$yrno++;

这两个里面的$1和$2是怎么确定的呢，前面没有出现过呀？


我刚学，所以问的问题比较菜，别见笑。

guap514

数括号

Ray001

print出来看看是啥值，就清楚了。

Perl_Er

回复 1# jinger18


   

Grouping Matching

From a regular-expression point of view, there is no difference between except, perhaps, that the former is slightly clearer.

$string =~ /(\S+)\s+(\S+)/;

and

$string =~ /\S+\s+\S+/;

However, the benefit of grouping is that it allows us to extract a sequence from a regular expression. Groupings are returned as a list in the order in which they appear in the original. For example, in the following fragment we have pulled out the hours, minutes, and seconds from a string.

my ($hours, $minutes, $seconds) = ($time =~ m/(\d+)\d+)\d+)/);

As well as this direct method, matched groups are also available within the special $x variables, where x is the number of the group within the regular expression. We could therefore rewrite the preceding example as follows:

$time =~ m/(\d+)\d+)\d+)/;
my ($hours, $minutes, $seconds) = ($1, $2, $3);

When groups are used in substitution expressions, the $x syntax can be used in the replacement text. Thus, we could reformat a date string using this:

#!/usr/bin/perl

$date = '03/26/1999';
$date =~ s#(\d+)/(\d+)/(\d+)#$3/$1/$2#;

print "$date";

This will produce following result
1999/03/26

兰花仙子

简单的说，就是捕获正则表达式的分组。
正则表达式用()进行分组。

jinger18

哦，好像看懂了。
呵呵，感觉perl挺难的，照着教程学了一遍感觉还是不会编程

bluewaterray

哦，好像看懂了。
呵呵，感觉perl挺难的，照着教程学了一遍感觉还是不会编程
jinger18 发表于 2010-03-30 22:07

    看看置顶贴里推荐的书吧，那样事半功倍

jinger18

恩，会的，谢谢。
现在是时间紧迫，必须先编出个程序来

MMMIX

哦，好像看懂了。
呵呵，感觉perl挺难的，照着教程学了一遍感觉还是不会编程
jinger18 发表于 2010-03-30 22:07

    你的问题在于你不会编程，而不是不会用 Perl, 这和 Perl 难不难完全扯不上关系。

jinger18

回复 9# MMMIX


    恩，我同意您的说法。但没办法，在实习考核中要一周编个程序，为了找工作，只能先走步捷径了