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How to check if environment variable is set using shell script?

If you are wondering how can we check whether an environment variable is set or not in the system, here are few methods :

1. Manually
a. Run “set” command on the shell prompt, it will list out all the variables set in the system :
# set
b. Run “echo” command on the shell to print the value of the environment variable :
# echo $<environment variable>

2. Through Shell Script
Let say we intent to check whether environment variable “envVar” is set or not?

a. Method 1 – checking if “envVar” is set to “” (no value) :
if [ "$envVar" == "" ]
then
echo “envVar is not set”
else
echo “envVar is set”
fi

b.Method 2 – checking if “envVar” is non NULL :
if [ -n "$envVar" ]
then
echo “envVar has non NULL value, it is set.”
else
echo “envVar has NULL value, it is not set.”
fi
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