bash脚本命令替换如何工作？ [英] How does bash script command substitution work?

问题描述

然而：为什么这个特定的脚本有这个结果？

从根据内获取Bash脚本的源目录https://stackoverflow.com/questions/59895/can-a-bash-script-tell-what-directory-its-stored-in#comment16925670_59895\">关于该问题的评论，我使用以下内容一个cron工作：

  DIR = $（pwd）
如果[$ CRON ==true];那么
＃如果环境变量$ CRON设置为true，我们可能在cron作业
中，如果[$ PWD ==/];那么
＃如果当前的工作目录是root，我们可能在cron工作中
 DIR =$（cd$（dirname$ {BASH_SOURCE [0]}）& & pwd&& echo x）
 DIR =$ {DIR％x}
 fi 
 fi 
  

$ b $ p $然而，我的目录变量（$ DIR）以某种方式结束了一个换行符，无论如何，随着$ DIR变量用于创建一个路径，它将中断脚本。为什么是换行？

诚然，我不太熟悉bash脚本和命令替换的细微差别。可能我误解了l0b0脚本的目的。

解决方案

简单：建议的代码是错误的，并且总是添加换行符因为pwd总是打印一个）。

更正的版本将是

  dir =$（cd$（dirname$ {BASH_SOURCE [0]}）&&& printf％sx$ PWD）
 dir = $ {dir％x} 
  

And: "Why does this particular script have this outcome?"

From Getting the source directory of a Bash script from within, based on some code snippets offered by user l0b0 in his comment on that question, I used the following for a cron job:

DIR=$(pwd)
if [ $CRON == "true" ]; then
  # If the environment variable $CRON is set to true, we're probably in a cron job
  if [ $PWD == "/" ]; then
    # And if the current working directory is root, we're probably in a cron job
    DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd && echo x)"
    DIR="${DIR%x}"
  fi
fi

However, my directory variable ($DIR) somehow ends up with a newline after it anyway, which breaks the script any time the $DIR variable is used to create a path. Why is the newline there?

Admittedly, I'm not overly familiar with the nuances of bash scripting and command substitution. It is possible I misunderstood the purpose behind l0b0's script.

解决方案

Simple: the suggested code is wrong and always adds a line feed (because pwd always prints one).

The corrected version would be

dir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && printf "%sx" "$PWD")"
dir=${dir%x}

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