`

To see the list of environment variables set by bash, run the env

command directly from the shell:

$ env

SHELL=/bin/bash

LANGUAGE=en_CA:en

DESKTOP_SESSION=ubuntu

PWD=/home/user

--snip—

You can read individual environment variables using the echo

command. For example, to print the default shell set for the user, use

the SHELL environment variable preceded by a dollar sign ($) and

surrounded by curly braces ({}). This will cause bash to expand the

variable to its assigned value, as shown in Listing 1-1.

$ echo ${SHELL}

/bin/bash

Listing 1-1

Printing an environment variable to the terminal

Table 1-2 shows a short list of some of the default environment

variables available.

Table 1-2

Bash Environment Variables

Variable name

What It Returns

BASH_VERSION

The bash version running

BASHPID

The process ID of the current bash process

GROUPS

A list of groups the running user is a member of

HOSTNAME

The name of the host

OSTYPE

The type of operating system

PWD

The current working directory

RANDOM

A random number between 0 and 32,767

UID

The user ID of the current user

SHELL

The full pathname to the shell

Try checking the values of these environment variables:

$ echo ${RANDOM}

8744

$ echo ${UID}

1000

$ echo ${OSTYPE}

linux-gnu

Black Hat Bash (Early Access) © 2023 by Dolev Farhi and Nick Aleks