Perl 移位运算符简单问题 [英] Perl shift operator simple question

问题描述

下面两行perl的目的是什么??

What's the purpose of the following two lines of perl??

my $host = shift || 'localhost';
my $port = shift || 200;

那应该返回 localhost 和端口 10.什么是 shift 关键字??

That should return localhost and port 10. What is the shift keyword??

推荐答案

这段代码是什么，是一种为 $host 和 $port 提供默认值的方法>.它通常位于脚本或子程序的开头，并分别从 @ARGV 和 @_ 获取值.

What this piece of code is, is a way to provide default values for $host and $port. It will typically be at the start of a script or a subroutine, and take values from @ARGV and @_ respectively.

那应该返回本地主机和端口10.

That should return localhost and port 10.

不，|| 运算符是一个短路OR，这意味着如果LHS 操作数返回真值，则RHS 操作数将被忽略.基本上，这意味着(并且仅此):如果为真，则选择左侧值，否则选择右侧值."

No, the || operator is a short circuiting OR, which means that if the LHS operand returns a true value, the RHS operand is ignored. Basically, it means this (and ONLY this): "choose the left hand side value if it is true, otherwise choose the right hand side value."

shift ARRAY 将返回ARRAY的第一个值，或者:

shift ARRAY will return the first value of ARRAY, or:

如果省略了 ARRAY，则移动 @_词法范围内的数组子程序和格式，以及@ARGV子程序外的数组以及在建立的词法范围内通过 eval STRING , BEGIN {} , INIT{} , 检查 {} , UNITCHECK {} 和 END{} 构造.

If ARRAY is omitted, shifts the @_ array within the lexical scope of subroutines and formats, and the @ARGV array outside a subroutine and also within the lexical scopes established by the eval STRING , BEGIN {} , INIT {} , CHECK {} , UNITCHECK {} and END {} constructs.

引自 http://perldoc.perl.org/functions/shift.html

当然，shift 还会从被移位的数组中移除值.因此，您可以像这样连续使用两个 shift，以便非常方便地处理参数.

Also, of course, shift removes the value from the array that is shifted. Therefore you can have two shift in a row like this, for very convenient argument handling.

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