(=) 符号后有空格的变量赋值? [英] Assignment of variables with space after the (=) sign?

问题描述

在 Bash 中，为变量赋值是使用 T=content 完成的，等号前后没有空格.

In Bash, assigning values to variables is done using T=content, with no spaces before or after the equal sign.

尽管我在 shell 脚本 PWD=/bin/pwd 中看到了以下内容，在等号的右侧包含一个空格.

Despite that I've seen the following in a shell script PWD= /bin/pwd containing a space on the right side of the equals sign.

它有一个空间的目的是什么?

What's the purpose of it have a space?

推荐答案

在例子PWD=/bin/pwd中，变量PWD被设置为空字符串在执行命令 /bin/pwd 之前.更改仅对该行生效.

In the example PWD= /bin/pwd, the variable PWD is set to the empty string before executing the command /bin/pwd. The change only takes effect for that line.

这对于出于运行命令的目的对变量进行临时更改非常有用，而不会影响原始值.另一个例子是使用 read 设置不同的 IFS 时:

This can be useful to make a temporary change to a variable for the purposes of running a command, without affecting the original value. Another example of this would be when using read, to set a different IFS:

IFS=, read a b c <<<"comma,separated,list"

这将字段分隔符设置为逗号，以便正确读取 a、b 和 c.在这一行之后，IFS 返回到默认值，因此脚本的其余部分不受影响.

This sets the field separator to a comma so that a, b and c are read correctly. After this line, IFS returns to the default value, so the rest of the script isn't affected.

也许在某些系统上，命令pwd的输出受变量PWD的值的影响，因此这样做可以防止PWD<引起的问题/code> 被其他地方覆盖.

Perhaps on some systems, the output of the command pwd is affected by the value of the variable PWD, so doing this prevents problems caused by PWD being overwritten elsewhere.

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