bash shell scripting HowTo - Linux / Unix Q & A from nixCraft

Bash Shell: Find Out If a Variable Is Empty Or Not

in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, Suse, UNIX last updated January 21, 2017

My shell script depends upon user input. How do I find out if a variable called $_JAIL path is empty under a Linux / Apple OS X / Unix like operating systems?

Bash Check If Shell Is Interactive or Not Under Linux / Unix Oses

in BASH Shell last updated November 5, 2012

How do I check in GNU/Bash if a shell is running in interactive mode or not while writing shell scripts?

Grep Include Only *.txt File Pattern When Running Recursive Mode

in BASH Shell, Linux, UNIX last updated October 25, 2012

I‘m using Debian Linux as my development workstation. I would like to search a directory called ~/projects/ recursively for “foo” word only for *.txt files. How do I search all text files in ~/projects/ for “foo” word using grep command?

Bash Shell: Check If A Function Exists Or Not (Find Out If a Function Is Defined Or Not)

in BASH Shell, Linux, UNIX last updated April 2, 2010

How do I determine if a function called foo() is already defined in a bash script or not? If a function called foo() is defined just call it or show an error message?