检查环境变量是否已经设置 [英] check if environment variable is already set

问题描述

我正在编写一个shell脚本，我必须在其中检查是否设置了环境变量，如果未设置，则必须对其进行设置.有什么方法可以检查shell脚本，是否已经设置了环境变量?

I am writing a shell script, where I have to check if environment variable is set, if not set then I have to set it. Is there any way to check in shell script, whether an environment variable is already set or not ?

推荐答案

[ -z "$VARIABLE" ] && VARIABLE="abc"

if env | grep -q ^VARIABLE=
then
  echo env variable is already exported
else
  echo env variable was not exported, but now it is
  export VARIABLE
fi

我想强调一下[ -z $VARIABLE ]是不够的，因为您可以拥有VARIABLE，但是它没有被导出.这意味着它根本不是环境变量.

I want to stress that [ -z $VARIABLE ] is not enough, because you can have VARIABLE but it was not exported. That means that it is not an environment variable at all.

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