我应该如何使用 Perl 的标量范围运算符? [英] How should I use Perl's scalar range operator?

问题描述

标量.."运算符的典型用法是什么?是只选择文本块吗?

What is the scalar ".." operator typical usage? Is it only selecting blocks of text?

我自己的有趣例子:

sub get_next {
    print scalar($$..!$$), "\n";
}

get_next for 1 .. 5;  # prints numbers from 1 to 5
get_next for 1 .. 5;  # prints numbers from 6 to 10

推荐答案

根据这里的问题，人们似乎几乎不知道它，但是，是的，我会说典型的用法是选择文本块，或者使用

People hardly seem to know about it based on questions here, but, yes, I'd say typical usage is selecting blocks of text, either with

while (<>) {
  print if /BEGIN/ .. /END/;
}

或

while (<>) {
  print if 3 .. 5; # prints lines 3 through 5
}

后者是检查输入行号($.)的语法糖

The latter is syntactic sugar for checking against the input line-number ($.)

... if $. == 3 .. $. == 5;

这暗示着奇怪的外观

#! /usr/bin/perl -l

for ($_ = 1; $_ <= 10; ++$_) {
  print if $_ == 4 .. $_ == 7;
}

上面程序的输出是

4
5
6
7

如果您有某种括号条件，请在 subs 中进行测试:

If you have some sort of bracketing condition, test for it in subs:

for (...) {
  do_foo($x,$y,$z) if begin($x) .. end($z);
}

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