修改Perl中字符串的最后兩個字符

Question

我正在尋找問題的解決方案：

我有NSAP地址，長度為20個字符：

39250F800000000000000100011921680030081D

我現在必須用F0替換此字符串的最后兩個字符，最終字符串應如下所示：

39250F80000000000000010001192168003008F0

我當前的實現會切掉最后兩個字符並將F0追加到它：

my $nsap = "39250F800000000000000100011921680030081D";

chop($nsap);

chop($nsap);

$nsap = $nsap."F0";

有沒有更好的方法來實現這一目標？

Answer 1

你可以使用substr ：

substr ($nsap, -2) = "F0";

要么

substr ($nsap, -2, 2, "F0");

或者你可以使用一個簡單的正則表達式：

$nsap =~ s/..$/F0/;

---

這是來自substr的手冊頁：

   substr EXPR,OFFSET,LENGTH,REPLACEMENT 
   substr EXPR,OFFSET,LENGTH  
   substr EXPR,OFFSET  
           Extracts a substring out of EXPR and returns it.
           First character is at offset 0, or whatever you've
           set $[ to (but don't do that).  If OFFSET is nega-
           tive (or more precisely, less than $[), starts
           that far from the end of the string.  If LENGTH is
           omitted, returns everything to the end of the
           string.  If LENGTH is negative, leaves that many
           characters off the end of the string.

現在，有趣的是， substr的結果可以用作左值，並被賦值：

           You can use the substr() function as an lvalue, in
           which case EXPR must itself be an lvalue.  If you
           assign something shorter than LENGTH, the string
           will shrink, and if you assign something longer
           than LENGTH, the string will grow to accommodate
           it.  To keep the string the same length you may
           need to pad or chop your value using "sprintf".

或者您可以使用替換字段：

           An alternative to using substr() as an lvalue is
           to specify the replacement string as the 4th argu-
           ment.  This allows you to replace parts of the
           EXPR and return what was there before in one oper-
           ation, just as you can with splice().

Answer 2

$nsap =~ s/..$/F0/;

用F0替換字符串的最后兩個字符。

Answer 3

使用substr（）函數：

substr( $nsap, -2, 2, "F0" );

chop（）和相關的chomp（）實際上是用於刪除行結束字符 - 換行符等。

我相信substr（）比使用正則表達式更快。