重击pwd并用管道打开不起作用 [英] Bash pwd and open with pipe not working

问题描述

我正在学习如何在bash中使用I/O重定向，并尝试了一些类似管道的示例:

I'm learning how to work with I/O Redirection in bash and tried some examples with the pipe like:

pwd | say
ls -l | grep "staff" > out.txt

但是当我尝试通过管道重定向同时使用pwd和open时，该命令将失败，并且我只会收到open的用法.

But when I try using both pwd and open using pipe redirection, the command fails and I just receive open usage.

我正在尝试的是:pwd | open

从bash打开当前目录的正确方法是什么?

What is the correct way to open the current directory from bash?

推荐答案

借助事后观察，有 2个不同的答案:

A:要回答OP的问题 ，以 了解管道和 I/O流 :

A: To answer the OP's question as asked with a view to understanding pipes and I/O streams:

echo . | xargs open

# Equivalent solution, using the special "$PWD" shell variable.
printf '%s\0' "$PWD" | xargs -0 open

是通过管道将当前目录路径传递到open CLI 的最健壮方法，以便在OSX的文件系统浏览器GUI应用程序.

is the most robust way to pass the current directory's path to the open CLI via a pipe in order to have it open that directory in OSX's file-system-browser GUI application, Finder.

^{请注意，pwd | xargs open并不健壮，因为如果当前目录路径具有嵌入式空格，它将失败-请参见下文.}

^{Note that pwd | xargs open is NOT robust, because it fails if the current directory path has embedded whitespace - see below.}

• open 要求输入是通过命令行参数 提供的，而不是通过 stdin输入流提供的，例如就是这种情况(通过管道|).
• 因此，为了将标准输入转换为参数，需要标准的 xargs实用工具.
• xargs 接受标准输入-在这种情况下来自管道-并调用指定为 its 参数(open， (在这种情况下)使用标记化的stdin输入作为该命令的自变量 .
• xargs默认按空白分隔:
  • 使用.作为输入，不会发生拆分(或由外壳解释)，因此可以将其拆分为xargs.
  • 相比之下，特殊的$PWD shell变量始终包含当前目录的完整路径，可能包含 embedded 空格，因此 extra需要采取步骤以确保将其作为单个参数传递给open:
    • printf '%s\0' "$PWD"打印当前目录.以NUL字节(0x0)终止的完整路径.
    • 互补地，xargs -0通过NUL将stdin输入拆分为令牌-在这种情况下，生成一个单个令牌，并保留单个输入行的值-包含$PWD- as是.这是安全的，因为NUL不是文件名中的合法字节.
      • 注意:-0是
      • open requires input to be provided via command-line arguments rather than via the stdin input stream, as is the case here (via a pipe, |).
      • Thus, in order to translate stdin input to arguments, the standard xargs utility is needed.
      • xargs takes stdin input - coming from a pipe in this case - and invokes the command specified as its argument (open, in this case) with the tokenized stdin input as that command's arguments.
      • xargs splits by whitespace by default:
        • With . as the input, no splitting (or interpretation by the shell) occurs, so it can just be echoed to xargs.
        • By contrast, the special $PWD shell variable, which always contains the current dir.'s full path, may contain embedded whitespace, so extra steps are needed to ensure that it's passed to open as a single argument:
          • printf '%s\0' "$PWD" prints the current dir.'s full path terminated with a NUL byte (0x0).
          • Complementarily, xargs -0 splits stdin input into tokens by NUL - resulting in a single token in this case, preserving the value of the single input line - containing $PWD - as is. This is safe to do, because NUL is not a legal byte in filenames.
            • Note: -0 is a nonstandard extension to the POSIX standard for xargs, but it's implemented in both BSD xargs (as aused on OSX) and GNU xargs (as used on Linux). Remaining POSIX-compliant^[1], the next best thing is to use line-based tokenizing with the -I option as follows:
              printf '%s' "$PWD" | xargs -I % open %

            因此，实际上上述解决方案与等效(xargs最终执行的操作-请参见下一节的解释):

            Thus, in effect the above solutions are equivalent to (what xargs ultimately executes - see next section for an explanation):

            open . 
            
            # Equivalent solution.
            open "$PWD"
            

            ^{[1] xarg的-I选项要求POSIX系统也为}

            ^{[1] xarg's -I option requires a POSIX system that is also XSI-compliant. If anyone can explain to me what that means in practical terms, I'd be grateful.}

            B:要为最佳答案提供不受技术限制的 :

            B: To provide the best answer with no constraints on techniques employed:

            open .
            

            open期望输入参数而不是stdin，并且.简洁有效地表示当前目录，从而导致open在.

            open expects arguments rather than stdin input, and . succinctly and most efficiently represents the current directory, causing open to display the contents of the current folder in Finder.

            等效但更冗长的解决方案是传递特殊的shell变量$PWD，该变量始终包含当前目录的完整路径(在 double 引号中引用，以防止它受到外壳扩展:

            An equivalent, but more verbose solution is to pass the special shell variable $PWD, which always contains the full path of the current directory (referenced in double quotes, so as to protect it from shell expansions:

            open "$PWD"
            

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