如何检查环境变量是否存在并获取其值? [英] How to check if an environment variable exists and get its value?

问题描述

我正在编写一个shell脚本.在此Shell脚本中，我有一个采用默认值或环境变量值的变量.但是，不必存在环境变量.

I am writing a shell script. In this shell script, I am have a variable that either takes a default value, or the value of an environment variable. However, the environment variable doesn't have to be present.

例如，假设在运行脚本之前，我执行了以下操作:

For instance, assume, before running the script, I perform the following operation:

export DEPLOY_ENV=dev

如何告诉脚本搜索此环境变量，并将其值存储在脚本内部的变量中.此外，如何告诉脚本如果该环境变量不存在，请存储默认变量?

How do I tell the script to search for this environment variable, and store its value in a variable inside the script. Moreover, how do I tell the script that if this environment variable does not exist, store a default variable?

推荐答案

[ -z "${DEPLOY_ENV}" ]检查DEPLOY_ENV的长度是否等于零.这样就可以运行:

[ -z "${DEPLOY_ENV}" ] checks whether DEPLOY_ENV has length equal to zero. So you could run:

if [[ -z "${DEPLOY_ENV}" ]]; then
  MY_SCRIPT_VARIABLE="Some default value because DEPLOY_ENV is undefined"
else
  MY_SCRIPT_VARIABLE="${DEPLOY_ENV}"
fi

# or using a short-hand version

[[ -z "${DEPLOY_ENV}" ]] && MyVar='default' || MyVar="${DEPLOY_ENV}"

# or even shorter use

MyVar="${DEPLOY_ENV:-default_value}"

这篇关于如何检查环境变量是否存在并获取其值?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！