redo 操作符

beyes

redo 操作符也用于控制循环，它不经过任何条件测试直接返回到本次循环的顶端，这种概念在 C 语言里并不存在。它和 next 的区别是，next 会正常继续下一次迭代，而 redo 则会重新执行这次迭代。比较下面的程序：

[Perl] 纯文本查看 复制代码

#!/usr/bin/perl

foreach (1..10) {
        print "Iteration number $_.\n\n";
        print "Please choose: last, next, redo, or none of the above? ";
        chomp (my $choice = <STDIN>);
        print "\n";
        last if $choice =~ /last/i;
        next if $choice =~ /next/i;
        redo if $choice =~ /redo/i;
        print "That wasn't any of the choices... onward~\n\n";
}
print "That's all, folks!\n";

运行输出：

# ./redo2.pl
Iteration number 1.

Please choose: last, next, redo, or none of the above? next

Iteration number 2.

Please choose: last, next, redo, or none of the above? next

Iteration number 3.

Please choose: last, next, redo, or none of the above? redo

Iteration number 3.

Please choose: last, next, redo, or none of the above? next

Iteration number 4.

Please choose: last, next, redo, or none of the above? ^C

由输出可见，在使用 redo 时，foreach 停止向前推进，而是在当前所在地重新开始。