Bash - check if string is empty

In this article, we would like to show you how to check if string is empty in Bash.

Practical example

In this example, we use -z operator to check if string length is zero inside the if statement.

script.sh file:

#!/bin/bash

string=""

if [ -z "$string" ]; then
    echo "The string is empty"
fi

Note: this approach should be used in POSIX shells where other solutions may not work.

Run in command line:

./script.sh

Output:

The string length is empty

Altermative notation

1. test based solution

#!/bin/bash

string=""

if test -z "$string"; then
    echo "The string is empty"
fi

Note: [ ] notation is shorthand of test command.

2. [[ ]] based solution

#!/bin/bash

string=""

if [[ -z "$number" ]]; then
    echo "The string is empty"
fi

Note: [[ ]] notation is like extended test command, adding additional features (e.g. regular expressions).

See also

1. Bash - check if string is not empty