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

Bash shell find out if a variable has NULL value OR not

last updated December 27, 2018 in BASH Shell, FreeBSD, Korn Shell Scripting, KSH Shell, Linux, UNIX

I am a new to shell scripting. How do I check for NULL value in a Linux or Unix shell scripts?

Bash Shell Find Out If a Variable Is Empty Or Not

last updated August 9, 2018 in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, Suse, UNIX

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? Can you tell me command on bash shell to find out if a variable is empty?

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

last updated November 5, 2012 in BASH Shell

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

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

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)

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

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?

BASH Shell Test If a File Is Writable or Not

last updated December 30, 2019 in AIX, BASH Shell, CentOS, Debian / Ubuntu, Fedora Linux, FreeBSD, HP-UX Unix, Linux, OpenBSD, Solaris-Unix, Suse, Ubuntu Linux, UNIX

How can you test if a file is writable under UNIX / Linux bash shell scripting and programming language?

Bash Append Text To a Variable

last updated February 4, 2013 in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, RedHat and Friends, Suse, Ubuntu Linux, UNIX

How do I append additional text a variable? For e.g., I’ve a vech set as follows:
vech=”London”

I’d like to add (append) “Bus” word to $vevh under UNIX scripting using bash?