Bash Check If Environment Variable Is Set

Using if-else with -z,-v,-n Options

Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the [-v HOME] will be true, and it will be true if the specified variable is set.

The -v option returns true if the given variable is set to an empty string, while it returns false if the provided variable is not declared.

Use the if-else statement with the -z option to check if the length of the environment variable is 0 in bash. Length 0 represents the unset variable. The echo command within the if block will be executed if the [ -z "${HOME}" ] will be true and it will be true if the length of the specified variable 0.

Alternatively, we can use the -z option with double square brackets. We don’t have to double-quote the variable using double square brackets with the -z option.

The -z option returns true if the variable is undeclared or initialized with an empty string.

Or, we can use the one-line solution as follows.

Use the if-else statement with -z and -v options to check if the environment variable is set, unset, or initialized with an empty string.

Use the if-else statement with the -n option to check if the environment variable is not empty. If it is not empty, the given variable is set; otherwise, unset.

Using Parameter Expansion

If you don’t have any concerns about the difference between an unset variable or the variable with an empty value, you can use the default-value parameter expansion as demonstrated below.

Here, we get an advantage of the parameter expansion, which used the ${parameter:-word} syntax to substitute the default value if the HOME environment variable is not set. Considering the above code, the ${parameter} is the parameter’s name, which is HOME in this case. The :- is an expansion operator that specifies if the parameter is null or unset, the default value should be used. Finally, the word is the default value if the parameter is null or unset.

So, if it is set, the echo "${HOME:-default_value}" printed the value of the HOME environment variable. On the other hand, if it is unset or null, the string default_value will be printed instead. This approach is useful when we want a default value if the provided variable is unset or undefined.

Let’s see another example to understand more clearly.

In contrast, if you do care about the difference between an unset variable or the variable with an empty value, then drop the colon.

Using printenv Command

Use the printenv command to print the current value of the specified environment variable in bash.

Use the printenv command to print the current value of all the environment variables in bash.

Further reading:

Check if Command Exists in Bash

Read more →

Bash Check If grep Result Is Empty

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Using env Command

Use the env command with the grep command to grab the specified environment variable with its current value in bash.

Use the env command to print the current value of all the environment variables in bash.

Using echo Command

Use the echo command with ${VARNAME:+VALUE} syntax to print the Variable is set message if the specified environment variable is set in bash. It will show nothing if the given variable is undeclared or initialized with an empty string.

Use the echo command with ${VARNAME} syntax to print the current value of the specified environment variable in bash. It will show nothing if the given variable is not declared or initialized with an empty string.

That’s all about how to check if environment variable is set in Bash.