`read`和`sysread`有什么区别？ [英] What is the difference between `read` and `sysread`?

问题描述

阅读 和< a href =http://perldoc.perl.org/functions/sysread.html =noreferrer> sysread 的文档非常相似。这两者有什么区别？

read and sysread have very similar documentation. What are the differences between the two?

推荐答案

关于 读取 ：

• read 支持PerlIO图层。


• 读取适用于任何Perl文件句柄 ^[1] 。


• 读取缓冲区。


• read 从8 KiB ^[2] 的固定大小的块中获取系统中的数据。


• read 可能会阻止可用的数据少于请求的数据 ^[3] 。

• read supports PerlIO layers.
• read works with any Perl file handle^[1].
• read buffers.
• read obtains data from the system in fixed sized blocks of 8 KiB^[2].
• read may block if less data than requested is available^[3].

关于 sysread ：

• sysread 不支持PerlIO图层（意味着它需要原始又名二进制句柄。。


• sysread 仅适用于映射到系统文件句柄/描述符^{的Perl文件句柄[4] 。}


• sysread 不缓冲。


• sysread 执行单个系统调用。


• sysread 如果可以返回数据，则立即返回如果数据量小于请求金额。

• sysread doesn't support PerlIO layers (meaning it requires a raw a.k.a. binary handle).
• sysread only works with Perl file handles that map to a system file handle/descriptor^[4].
• sysread doesn't buffer.
• sysread performs a single system call.
• sysread returns immediately if data is available to be returned, even if the amount of data is less than the amount requested.

摘要和结论：

• 读取适用于任何Perl文件句柄，而 sysread 仅限于映射到系统文件句柄/描述符的Perl文件句柄。


• 读取与 选择 ^[5] ，同时 sysread 与兼容。


• read 可以为您执行解码，而 sysread 则要求您自行解码。


• <$ c对于非常小的读取，$ c> read 应该更快，而 sysread 应该是紧固的r用于较大的读数。

• read works with any Perl file handle, while sysread is limited to Perl file handles mapped to a system file handle/descriptor.
• read isn't compatible with select^[5], while sysread is compatible with select.
• read can perform decoding for you, while sysread requires that you do your own decoding.
• read should be faster for very small reads, while sysread should be faster for larger reads.

注意：

1. 这些包括，例如，绑定文件句柄和使用 open创建的句柄（我的$ fh，'<'，\ $ var ）。

在5.14之前，Perl读入了4个KiB块。从5.14开始，当您构建 perl 时，块的大小是可配置的，默认值为8 KiB。

Before 5.14, Perl read in 4 KiB blocks. Since 5.14, the size of the blocks is configurable when you build perl, with a default of 8 KiB.

根据我的经验，从普通文件读取时，读取将准确返回请求的数量（如果可能），但从管道读取时可能返回更少。这些结果无法保证。

In my experience, read will return exactly the amount requested (if possible) when reading from a plain file, but may return less when reading from a pipe. These results are by no means guaranteed.

fileno 会返回这些值的非负数。例如，这些包括从普通文件，管道和套接字读取的句柄，但不包括[1]中提到的句柄。

fileno returns a non-negative number for these. These include, for example, handles that read from plain files, from pipes and from sockets, but not those mentioned in [1].

我指的是由 IO :: Select 调用的4个参数。

I'm referring to the 4-argument one called by IO::Select.

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