$ PWD与有关PWD可移植性 [英] $PWD vs. pwd regarding portability

问题描述

我在写一个shell脚本，分析当前工作目录的路径（打印像所有基本名的当前目录以上）。

到目前为止，我一直在使用环境变量 PWD 来解析路径，但我不知道是否

• 我可以在 PWD 来始终设置
计数

• 要给予同样的结果每个平台上

难道可能是更好的使用 PWD 壳内置？我需要这个脚本运行在尽可能多的平台，尽可能，所以我只是想知道...

解决方案

POSIX 要求 $ PWD 在以下方式进行设置：

  PWD
 

此变量应当重新present当前工作目录的绝对路径。它不应包含在点或点 - 点的任何组件。该值是由CD实用程序初始化期间设置，并通过用sh效用

所以，你可以依赖于被设置＆ndash的;但千万注意......绝对路径...，没有的的的绝对路径。

庆典（至少最近的版本）会记得什么符号链接，你跟着当设置 $ PWD （和 PWD 内置）。 pwd命令（即外部命令）不会。所以，你会得到不同的结果出现，这可能会，也可能不会，对你很重要。使用 PWD -P 如果你想在不符号链接的路径。

请注意， PWD 文档状态：

  

如果应用程序设置或取消设置PWD的值，PWD的行为是不确定的。

所以，千万不要做：）

总之，这里没有赢家。环境变量将在那里在POSIX的壳，作为将外部指令和可能一个内置的太。选择最适合您的需要，是你是否关心符号链接与否最重要的事情之一。

I'm writing a shell script which parses the path of the current working directory (printing a like of all basenames above the current directory).

So far, I've been using the environment variable PWD to parse the path but I wonder if

• I can count on PWD to be always set
• to give the same result on every platform

Would it possibly be better to use the pwd shell-builtin? I need this script to run on as many platforms as possible, so I just wondered...

解决方案

POSIX requires $PWD to be set in the following fashion:

PWD  

This variable shall represent an absolute pathname of the current working directory. It shall not contain any components that are dot or dot-dot. The value is set by the cd utility, and by the sh utility during initialization.

So you can rely on that being set – but do note "... an absolute path...", not the absolute path.

bash (at least recent versions) will remember what symlinks you followed when setting $PWD (and the pwd builtin). command pwd (that is, the external command) will not. So you'll get different results there, which might, or might not, be important for you. Use pwd -P if you want a path without symlinks.

Do note that the pwd documentation states:

If an application sets or unsets the value of PWD, the behavior of pwd is unspecified.

So, don't do that :)

In short, there is no winner here. The environment variable will be there in POSIX shells, as will the external command and possibly a built-in too. Choose the one that best fits your need, the important thing being whether you care about symlinks or not.

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