Variables in Bash script

Variables in Bash script language have following properties:

• They haven't data type
• There is no need to declare variable

So, let's see how they works on simple "Hello World" Example:

#!/bin/bash
Var1 = "Hello World!"
echo $Var1

This simple example will output sentence Hello World!

 Interesting with $ sign in Bash is, if you put something in brackets after $ this will be interpreted as interpreter command.

#!/bin/bash
Var1= $(ls -la)
echo $Var1

This simple example will put output from ls -la command in $Var1 variable and then print content on screen.

Important thing about variables is that you can use local variables in functions, using keyword local.

local Var1="Local variable"

Builtin variables

 

 Bash have Built-in variables, some of them are:

• $BASH - Path to the Bash binary
• $BASHPID - Process ID of Bash 
• $BASH_VERSION - Version of Bash
• $HOME - Home directory of user
• $MACHTYPE - Machine type
• $PATH - Path to binaries
• $PWD - Working directory
• $SECONDS - number of second while script is running
• $UID - User ID number
• $0,$1 ... - Command line arguments
• $# - Number of command line arguments

And many more...