Bash if null check

Collectives on Stack Overflow. Learn more. Checking for null string in bash Ask Question. Asked 10 years, 6 months ago. Active 10 years, 6 months ago. Viewed 7k times. Is there any difference between the following tests? Add a comment. Active Oldest Votes. Nope, they are all the same.

But couple of defensive habits to get into. Viewed k times. Improve this question. Sylvain Pineau You should provide 1. You should use [[ ]]. Otherwise you have to quote your variables. WinEunuuchs2Unix Not necessarily irrelevant - in some cases you want to ensure there's actually something instead of blank or null string in arguments.

Add a comment. Active Oldest Votes. Improve this answer. Sylvain Pineau Sylvain Pineau It works for me! When writing portable shell scripts, this flag should be used with care, since on certain commercial Unixes this flag is faulty.

See my answer for linked sources. Community Bot 1. Avinash Raj Avinash Raj You have to use other test constructs instead like -a , I think — muru. Guariba Som Guariba Som 31 2 2 bronze badges. However, in all 3 cases the issue is the same - unset variable will be treated as empty, thus what the shell sees with these unquoted variables is [!

Ro Yo Mi 3 3 bronze badges. Sergiy Kolodyazhnyy Sergiy Kolodyazhnyy Whenever we are working with strings in Bash, it is very important for us to check if a string is null or not so that it cannot cause any problem in the execution of our program.

First, we will create a Bash file in our Home directory named Strings. After creating this file, we will type the script shown in the following image in our file. Like every Bash script, the first line, i. We will type the following script in our Bash file.

The script for this scenario is almost the same as for the scenario discussed above.