请帮助解释一下，不太明白！

cheng_ge

内容如下：
#!/usr/bin/perl

$maxLenth=100;
@a = (0..9,'$','%','a'..'z','A'..'Z','-','+','_');
$password = join '', map { $a[int rand @a] } 0..($maxLenth-1);
print "$password\n";


主要是第五行！说高手指点

cheng_ge

http://blog.chinaunix.net/u/10363/showart.php?id=53084  

哈哈，5.产生随机密码！

谢，仙子姐姐？？！！

flw

1. join EXPR,LIST
   
2.         Joins the separate strings of LIST into a single string with
   
3.         fields separated by the value of EXPR, and returns that new
   
4.         string. Example:
   
5. 
   
6.             $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
   
7. 
   
8.         Beware that unlike "split", "join" doesn't take a pattern as its
   
9.         first argument. Compare "split".

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备忘：join 将 LIST 里面的每个元素用 EXPR 为分隔符连接成一个字符串，并且返回这个字符串

1. map BLOCK LIST
   
2. map EXPR,LIST
   
3.         Evaluates the BLOCK or EXPR for each element of LIST (locally
   
4.         setting $_ to each element) and returns the list value composed
   
5.         of the results of each such evaluation. In scalar context,
   
6.         returns the total number of elements so generated. Evaluates
   
7.         BLOCK or EXPR in list context, so each element of LIST may
   
8.         produce zero, one, or more elements in the returned value.
   
9. 
   
10.             @chars = map(chr, @nums);
    
11. 
    
12.         translates a list of numbers to the corresponding characters.
    
13.         And
    
14. 
    
15.             %hash = map { getkey($_) => $_ } @array;
    
16. 
    
17.         is just a funny way to write
    
18. 
    
19.             %hash = ();
    
20.             foreach $_ (@array) {
    
21.                 $hash{getkey($_)} = $_;
    
22.             }
    
23. 
    
24.         Note that $_ is an alias to the list value, so it can be used to
    
25.         modify the elements of the LIST. While this is useful and
    
26.         supported, it can cause bizarre results if the elements of LIST
    
27.         are not variables. Using a regular "foreach" loop for this
    
28.         purpose would be clearer in most cases. See also "grep" for an
    
29.         array composed of those items of the original list for which the
    
30.         BLOCK or EXPR evaluates to true.
    
31. 
    
32.         "{" starts both hash references and blocks, so "map { ..." could
    
33.         be either the start of map BLOCK LIST or map EXPR, LIST. Because
    
34.         perl doesn't look ahead for the closing "}" it has to take a
    
35.         guess at which its dealing with based what it finds just after
    
36.         the "{". Usually it gets it right, but if it doesn't it won't
    
37.         realize something is wrong until it gets to the "}" and
    
38.         encounters the missing (or unexpected) comma. The syntax error
    
39.         will be reported close to the "}" but you'll need to change
    
40.         something near the "{" such as using a unary "+" to give perl
    
41.         some help:
    
42. 
    
43.             %hash = map {  "\L$_", 1  } @array  # perl guesses EXPR.  wrong
    
44.             %hash = map { +"\L$_", 1  } @array  # perl guesses BLOCK. right
    
45.             %hash = map { ("\L$_", 1) } @array  # this also works
    
46.             %hash = map {  lc($_), 1  } @array  # as does this.
    
47.             %hash = map +( lc($_), 1 ), @array  # this is EXPR and works!
    
48. 
    
49.             %hash = map  ( lc($_), 1 ), @array  # evaluates to (1, @array)
    
50. 
    
51.         or to force an anon hash constructor use "+{"
    
52. 
    
53.            @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end
    
54. 
    
55.         and you get list of anonymous hashes each with only 1 entry.

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备忘：map 将 LIST 中的每个元素用 EXPR 或者 BLOCK 指定的代码处理一遍，并且返回处理后的列表。

1. rand EXPR
   
2. rand    Returns a random fractional number greater than or equal to 0
   
3.         and less than the value of EXPR. (EXPR should be positive.) If
   
4.         EXPR is omitted, the value 1 is used. Currently EXPR with the
   
5.         value 0 is also special-cased as 1 - this has not been
   
6.         documented before perl 5.8.0 and is subject to change in future
   
7.         versions of perl. Automatically calls "srand" unless "srand" has
   
8.         already been called. See also "srand".
   
9. 
   
10.         Apply "int()" to the value returned by "rand()" if you want
    
11.         random integers instead of random fractional numbers. For
    
12.         example,
    
13. 
    
14.             int(rand(10))
    
15. 
    
16.         returns a random integer between 0 and 9, inclusive.
    
17. 
    
18.         (Note: If your rand function consistently returns numbers that
    
19.         are too large or too small, then your version of Perl was
    
20.         probably compiled with the wrong number of RANDBITS.)

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备忘：rand 返回一个介于 0～EXPR 之间的随机的小数。

1. int EXPR
   
2. int     Returns the integer portion of EXPR. If EXPR is omitted, uses
   
3.         $_. You should not use this function for rounding: one because
   
4.         it truncates towards 0, and two because machine representations
   
5.         of floating point numbers can sometimes produce counterintuitive
   
6.         results. For example, "int(-6.725/0.025)" produces -268 rather
   
7.         than the correct -269; that's because it's really more like
   
8.         -268.99999999999994315658 instead. Usually, the "sprintf",
   
9.         "printf", or the "POSIX::floor" and "POSIX::ceil" functions will
   
10.         serve you better than will int().

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备忘：int 可以舍弃一个小数的小数部分，只留下整数部分。

合起来就是：

1. 得到一个由 $maxLength 个随机字符组成的字符串。该字符串中的每个字符都取自于 @a 这个字符数组。

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cheng_ge

真详细！ 非常感谢！！