How to check if an environment variable exists and get its value

Question

Below is the operation, I perform before I run the script: 

export DEPLOY_ENV=dev

When I run the script, I want to have a variable in the shell script which takes the default value when the environment variable is not present. If it’s present it has to store its value in a variable. Can anyone tell me how to do it? 

Answer 1

[ -z "${DEPLOY_ENV}" ] to check whether DEPLOY_ENV has a length equal to zero. See the below code: 

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}"

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