Black Hat Bash - Bash Scripting for Hackers and Pentesters (Early Access) (Dolev Farhi, Nick Aleks)

we wanted to change this script so that we first check that we have

enough space on the disk before attempting to create new files and

directories? Or what if we checked whether the directory and file

creation actions actually succeeded? This section and the next

chapter introduce you to the syntactical elements you’ll need to

accomplish these tasks.

Variables

Every scripting language has variables. Variables are names we

assign to memory locations that hold some value, and they act like

placeholders or labels. We can directly assign values to variables or

execute bash commands and store their output as variable values to

use for various purposes.

If you’ve worked with programming languages, you may know

that variables can be of different types, such as integers, strings, and

arrays. In bash, variables are untyped; they’re all considered

character strings. Even so, you’ll see that bash allows you to create

arrays, access array elements, or perform arithmetic operations so

long as the variable value consists of only numbers.

The following rules govern the naming of bash variables:

•^{They can include alphanumeric characters.}

•^{They cannot start with a numerical character.}

•^{They can contain an underscore (}^_^).

•^{They cannot contain whitespace.}

Assigning and Accessing Variables

Let’s assign a variable. Open a terminal and enter the following

directly in the command prompt:

$ book="black hat bash"

We create a variable named book, and by using the equal sign

(=), assign the value black hat bash to it. Now we can use this

variable in some command. For example, here we use the echo

command to print the variable to the screen:

$ echo "This book's name is ${book}"

This book's name is black hat bash