誰能解釋一下perl的規(guī)則式的意思？

paub

#!/usr/bin/perl
use strict;
use warnings;

my $string1 = "madam im adam";
my $string2 = "the motto means something";
my $string3 = "no palindrome here";

findPalindrome( $string1 );
findPalindrome( $string2 );
findPalindrome( $string3 );

sub findPalindrome
{
   my $string = shift();

   if ( $string =~
           /(\w)\W*(\w)\W*(\w)\W*(\w)\W*\4\W*\3\W*\2\W*\1/
        or $string =~
           /(\w)\W*(\w)\W*(\w)\W*(\w)\W*\3\W*\2\W*\1/ ) {
      print "$string - ",
            "has a palindrome of at least 7 characters.\n";
   }
   else {
      print "$string - has no long palindromes.\n";
   }
}

那位大俠能解釋一下：/(\w)\W*(\w)\W*(\w)\W*(\w)\W*\4\W*\3\W*\2\W*\1/和/(\w)\W*(\w)\W*(\w)\W*(\w)\W*\3\W*\2\W*\1/的意思

upperc

看不懂，學(xué)習(xí)一下 �。�！

changejun

建議樓主去本版的精華部分了解下perl的正則表達式吧！
你這正則表達式挺簡單的！

cobrawgl

這個正則式用來判斷字符串

has a palindrome of at least 7 characters

或者

has no long palindromes

人家自己說的很清楚嘛

paub

為什么不能講一下呢？不要吝嗇嗎。

paub

原帖由 cobrawgl 于 2008-5-4 16:42 發(fā)表
這個正則式用來判斷字符串

has a palindrome of at least 7 characters

或者

has no long palindromes

人家自己說的很清楚嘛

只是想有人給詳細的解釋一下，那2個表達式的意思。虛心向大家請教。謝謝！主要是后面的\4 \3 \2 \1不太明白。

[ 本帖最后由 paub 于 2008-5-4 16:47 編輯 ]

cobrawgl

Learning Perl 4th version

8.6. The Match Variables
So far, when we've put parentheses into patterns, they've been used only for their ability to group parts of a pattern together. But parentheses also trigger the regular expression engine's memory. The memory holds the part of the string matched by the part of the pattern inside parentheses. If there are more than one pair of parentheses, there will be more than one memory. Each regular expression memory holds part of the original string, not part of the pattern.

Since these variables hold strings, they are scalar variables; in Perl, they have names like $1 and $2. There are as many of these variables as there are pairs of memory parentheses in the pattern. As you'd expect, $4 means the string matched by the fourth set of parentheses.

1. 
   
2. /(\w)  ----> \1 or $1
   
3. \W*
   
4. (\w)  ----> \2 or $2
   
5. \W*
   
6. (\w)  ----> \3 or $3
   
7. \W*
   
8. (\w)  ----> \4 or $4
   
9. \W*
   
10. \4
    
11. \W*
    
12. \3
    
13. \W*
    
14. \2
    
15. \W*
    
16. \1/
    

復(fù)制代碼

cobrawgl

perl 還會提醒你，\1 最好寫成 $1 之類的。