如何取字符串内含有不确定字符的子串

nf1s

例：ABCDNXXXXNID
其中：XXXX是四位的数字，是可变的。并且NXXXX的位置也是不固定的。
我想将NXXXX这个字串取出来放在一个变量里备用。

正则表达式倒是可以匹配出NXXXX，但是我不知道如何将这个子串取出。

nf1s

问题已解决。

perldoc perlretut

Grouping things and hierarchical matching
Extracting matches

这里面有详细的说明。摘抄如下：
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Extracting matches

The grouping metacharacters "()" also serve another completely differ-
ent function: they allow the extraction of the parts of a string that
matched.  This is very useful to find out what matched and for text
processing in general.  For each grouping, the part that matched inside
goes into the special variables $1, $2, etc.  They can be used just as
ordinary variables:

        # extract hours, minutes, seconds
        $time =~ /(\d\d)\d\d)\d\d)/;  # match hh:mm:ss format
        $hours = $1;
        $minutes = $2;
        $seconds = $3;

Now, we know that in scalar context, "$time =~ /(\d\d)\d\d)\d\d)/"
returns a true or false value.  In list context, however, it returns
the list of matched values "($1,$2,$3)".  So we could write the code
more compactly as

         # extract hours, minutes, seconds
         ($hours, $minutes, $second) = ($time =~ /(\d\d)\d\d)\d\d)/);

If the groupings in a regexp are nested, $1 gets the group with the
leftmost opening parenthesis, $2 the next opening parenthesis, etc.
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