为什么使用自动化文件句柄的三参数公开调用是Perl的最佳实践？ [英] Why is three-argument open calls with autovivified filehandles a Perl best practice?

问题描述

我有两个关于Perl 打开函数的问题： 打开的三参数版本比两个参数版本更好，例如

  open（OUT，'>>'，$ file）; 
  

vs。

  open（OUT，>> $ file）; 
  

这是为什么？我曾试图告诉某人使用三参数版本，但似乎无法支持任何事情。

2）我似乎也记得autovivified文件句柄被优先于裸字文件句柄（他们称之为不同的东西）？也不记得为什么，例如

  open（my $ out，'>>'，$ file）; 
  

vs。

  open（OUT，'>>'，$ file）; 
  

它是严格的东西吗？我似乎记得可以使用 OUT 与 strict ，但我不记得。

$ b对于文件句柄使用typeglobs（如 OUT ）不是一个好主意，因为它们在你的整个程序中是全局的 - 你需要确保没有其他例程包括模块中的那些例程使用相同的名字（包括将来）。

使用开放式的双参数形式将您的应用程序暴露给由包含特殊字符的变量引起的错误行为，例如 my $ f;打开$ f，> $ some_filename; 暴露在 $ some_filename 包含前导>

使用三参数形式避免了这一点，方法是将模式和文件名分开的参数，他们不能干涉。

此外，使用管道参数形式是一个非常好的主意：

 打开$ pipe，'|  - '，'sendmail'，'[e-mail]'; 
  

比单个字符串更好 - 它避免了可能的shell注入等。 >

I've got two questions about the Perl open function:

1) I seem to remember from Perl Best Practices that the 3-argument version of open is better than the two argument version, e.g.

open(OUT, '>>', $file);

vs.

open(OUT, ">>$file");

Why is that? I was trying to tell somebody to use the 3-argument version the other day but couldn't seem to back it up with anything.

2) I also seem to remember autovivified filehandles being favored over bareword filehandles (they called something different)? And also couldn't remember why, e.g.

open(my $out, '>>', $file);

vs.

open(OUT, '>>', $file);

Is it a strict thing? I seem to remember being able to use OUT with strict but I can't remember.

解决方案

• Using typeglobs for filehandles (like OUT) is not a good idea, as they are global across your entire program - you need to be sure that no other routine including those in modules are using the same name (including in the future).
• Using the two-argument form of open exposes your application to mis-behaviour caused by variables containing special characters, for example my $f; open $f, ">$some_filename"; is exposed to the bug where $some_filename containing a leading > will change the program's behaviour.

Using the three-argument form avoids this by separating the mode and filename into separate arguments where they can't interfere.

Moreover, using the lots-of-arguments form with pipes is a very good idea:

open $pipe, '|-', 'sendmail', '[e-mail]';

Is better than doing it all as a single string – it avoids possible shell injection etc.

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