Skip to content.

Bash – set default value if a variable is empty By admin on Dec 16, 2015 There are multiple ways to check if a variable is empty and then set it to some default value. Here are two variables: A=$(cat ${FICHIER_BROKERS} | grep ${DATABASE_NAME} | grep dbo.$ You can quickly test for null or empty variables in a Bash shell script.

If the result is empty, then either the variable was empty, or; removing the leading spaces made it empty. This tutorial aims to help the reader understanding conditions in bash, and provides a […]


I want to check if this varaible is empty or not. Check to see if a variable is empty or not. If you use bash for scripting you will undoubtedly have to use conditions a lot, for example for an if … then construct or a while loop. Create a new bash file, named, and enter the script below. While working with bash shell programming, when you need to read some file content. Parameter substitute is another way to check the variable is set or unset. Bash Shell Find Out If a Variable Is Empty - Determine if a bash shell variable is empty or not using if or conditional expression under Linux/Unix/macOS. My shell script depends upon user input. In addition to set -u , bash's various forms of parameter expansion can also distinguish between unset and null values: ${foo:bar} expands to "bar" when foo is unset, but "" when foo is null, while ${foo:-bar} expands to "bar" if foo is unset or null. This article will help you to test if the file exists or not and the file is empty or not. You need to pass the -z or -n option to the test command or to the if command or use conditional expression. Line 6 - The backslash ( \ ) in front of the single quote ( ' ) is needed as the single quote has a special meaning for bash and we don't want that special meaning. An empty string can be created in DOS Scripting by assigning it no value during it’s initialization as shown in the following example. Also, since any bash test without an argument will always return true, it is advisable to quote the variables so that the test will have at least an (empty) argument, irrespective of whether the variable is set or not. This will safe your script from throwing errors. It's just an unquoted empty string. – chepner Sep 4 '12 at 14:28 11.

Set a= To check for an existence of an empty string, you need to encompass the variable name in square brackets and also compare it against a value in square brackets as shown in the following example. How do I check for NULL value in a Linux or Unix shell scripts? This is generally not a problem here because the script has been designed like this from the beginning.

Running drupal as root in order for it to run bash scripts. I have an ancient bash script that I'd like to improve. The -n operator checks whether the string is not null.

As I think this can happen to others, I decided to convert the php empty function in bash According to the php manual: a variable is considered empty if it doesn't exist or if its value is one of the following: "" (an empty string) 0 (0 as an integer) 0.0 (0 as a float) "0" (0 as a string) an empty array; a variable declared, but without a value
The question asks how to check if a variable is an empty string and the best answers are already given for that.. Therefore, if the test is true, the variable was either empty already or only had spaces inside it. Example-1: Check the variable is set or unset using ‘-z’ option.