`read` 和 `sysread` 有什么区别?

问题描述

read 和 sysread 有非常相似的文档.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 read:

• read 支持 PerlIO 层.
• read 适用于任何 Perl 文件句柄.
• 读取缓冲区.
• read 以 8 KiB 的固定大小块的形式从系统获取数据.
• read 如果可用数据少于请求的数据，则可能会阻塞.

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

关于sysread:

• sysread 不支持 PerlIO 层(意味着它需要一个原始的也就是二进制句柄).
• sysread 仅适用于映射到系统文件句柄/描述符的 Perl 文件句柄.
• sysread 不缓冲.
• sysread 执行单个系统调用.
• sysread 如果数据可返回，则立即返回，即使数据量少于请求的数量.

• 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.
• 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.

总结和结论:

• read 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.
• read 与 select，而 sysread 与 select 兼容.
• read可以为你解码，而sysread需要你自己解码.
• read 对于非常小的读取应该更快，而 sysread 对于非常大的读取应该更快.

• 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, 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 very large reads.

注意事项:

1. 例如，这些包括绑定文件句柄和使用 open(my $fh, '<', $var) 创建的文件句柄.

在 5.14 之前，Perl 读取 4 KiB 块.从 5.14 开始，构建 perl 时可以配置块的大小，默认为 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，read 在从普通文件读取时将准确返回请求的数量(如果可能)，但在从管道读取时可能返回较少.绝不保证这些结果.

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 返回一个非这些的负数.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] 中提到的那些.

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 IO::选择.

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