管道和文件重定向的区别-BASH [英] Difference in pipe and file redirection - BASH

问题描述

重定向用于重定向stdout/stdin/stderr！例如: ls>log.txt.

管道用于将命令的输出作为另一个命令的输入.例如: ls |grep file.txt

为什么这两个操作员确实在做同一件事?

为什么不只写 ls>grep 传递输出，这不只是一种重定向吗?

我意识到Linux是做一件事，做得好"，因此我必须缺少更多的逻辑原因.

解决方案

您要做需要区别对待的语法功能-并使用> 与 | 就可以了.

如果您在两种情况下都使用过> ，您怎么知道是否

  ls>grep 

试图写入名为 grep 的文件还是将输入发送到 grep 命令?>

^{grep 也许不是最好的例子，因为您可能会因为存在 grep 的强制性参数而产生歧义.但是，确实存在(可选)无参数的命令，例如 column .
其他人在评论中提供了另一个示例: test 可能是指测试输出文件或标准 test 命令 .}

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另一种查看方式:

您的建议实质上是将> 用作通用的send-output-somewhere运算符，而不考虑目标的类型(文件还是命令).

但是，只有转移了消除歧义的必要，然后在指定 target 时必须消除歧义-它是要输出到的文件还是要运行的命令?

考虑到简单命令的 first 令牌- foo [...] ，该外壳还具有隐式消歧功能.code>只会调用 command -在 operator -> 级别进行区分以输出到文件 | 是明智的选择.

Redirection is used to redirect stdout/stdin/stderr! Ex: ls > log.txt.

Pipes are used to give the output of a command as input to another command. Ex: ls | grep file.txt

Why exactly are these two operators doing the same thing?

Why not just write ls > grep to pass the output through, isn't this just a kind of redirection also?

I realize Linux is "Do one thing and do it well", so there has to be more of a logical reason that I'm missing.

解决方案

You do need a differentiating syntax feature - and using > vs. | will do just fine.

If you used > in both scenarios, how would you know whether

ls > grep

is trying to write to a file named grep or send input to the grep command?

^{grep is perhaps not the best example, as you may then be tempted to disambiguate by the presence of grep's mandatory arguments; however, (optionally) argument-less commands do exist, such as column.
that other guy offers another example in the comments: test may refer to a test output file or to the argument-less invocation of the standard test command.}

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Another way of looking at it:

Your suggestion is essentially to use > as a generic send-output-somewhere operator, irrespective of the type of target (file vs. command).

However, that only shifts the need for disambiguation, and then you have to disambiguate when specifying the target - is it a file to output to or a command to run?

Given that the shell also has an implicit disambiguation feature when it comes to the first token of a simple command - foo [...] only ever invokes a command - differentiating at the level of the operator - > for outputting to files, | for sending to commands - is the sensible choice.

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