Perl CORE::say vs -E [英] Perl CORE::say vs -E

问题描述

在这个答案中使用perl one-liner as:

In this answer is used the perl one-liner as:

perl -we '... CORE::say "x=$x"'

使用 -e 和 CORE::say 而不是较短的:-E 和普通的 say 有什么好处，例如:

What is the advantage using the -e and CORE::say instead of the shorter: -E and plain say, e.g.:

perl -wE '... say "x=$x"'

推荐答案

feature.pm was引入以允许向 Perl 添加向后不兼容的功能.-E 启用所有向后不兼容的功能，这意味着如果升级 perl，使用 -E 的程序可能会崩溃.

feature.pm was introduced to allow backwards-incompatible features to be added to Perl. -E enables all backward-incompatible features, which means a program that uses -E may break if you upgrade perl.

perl               -E'... say "foo";       ...'   # Forward-incompatible (5.10+)
perl -Mfeature=say -e'... say "foo";       ...'   # ok (5.10+)
perl -Mv5.10       -e'... say "foo";       ...'   # ok (5.10+)
perl -M5.010       -e'... say "foo";       ...'   # ok (5.10+)
perl               -e'... CORE::say "foo"; ...'   # ok (5.16+)

<小时>

例如，假设您在 2010 年编写了以下程序:

---

For example, say you wrote the following program in 2010:

perl -E'sub fc { my $acc=1; $acc*=$_ for 2..$_[0]; $acc } say fc(5);'

使用 2010 年最新的 Perl (5.12)，程序输出如下:

With the latest Perl in 2010 (5.12), the program outputs the following:

120

使用 2016 年最新的 Perl (5.24)，程序输出如下:

With the latest Perl in 2016 (5.24), the program outputs the following:

5

不同之处在于 5.16 添加了一项功能，该功能在启用时会更改该程序的含义.如果避免使用-E，程序的行为就不会改变.具体来说，5.24中的输出120:

The difference is due to the addition of a feature to 5.16 that changes the meaning of that program when enabled. If one had avoided the use of -E, the program's behaviour would not have changed. Specifically, the following outputs 120 in 5.24:

perl -e'sub fc { my $acc=1; $acc*=$_ for 2..$_[0]; $acc } CORE::say fc(5);'

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