07_environment.md

Environment

The shell environment is configured through a variety of variables called environment variables. This environment tells the shell and your various tools how to behave.

Try this now:

BabyMac:~ jennapederson$ env

This prints out the environment in its current state.

To Set a Variable for a Process

Let’s edit the hello_world.sh file using vim to use a variable:

#!/bin/bash
echo "Hello World, $HELLO_WORLD_NAME!"

Try this now ex. 2:

BabyMac:~ jennapederson$ HELLO_WORLD_NAME='Jenna Pederson' ./hello_world.sh
Hello World, Jenna Pederson!
BabyMac:~ jennapederson$ env | grep HELLO_WORLD_NAME
BabyMac:~ jennapederson$ echo $HELLO_WORLD_NAME

To Set a Variable for the Current Session

You can also set variables that are available for the duration of your current session.

Try this now ex. 2:

BabyMac:~ jennapederson$ export HELLO_WORLD_NAME='Jenna Pederson'
BabyMac:~ jennapederson$ env | grep HELLO_WORLD_NAME
HELLO_WORLD_NAME=Jenna Pederson
BabyMac:~ jennapederson$ ./hello_world.sh
Hello World, Jenna Pederson!

To make environment variables persistent across login, you must export them on login. To do this, they need to be added to your ~/.bashrc file, which is sourced (executed) when you login. We’ll take a look at this with a later example.

To Unset a Variable

Try this now:

BabyMac:~ jennapederson$ unset HELLO_WORLD_NAME
BabyMac:~ jennapederson$ env | grep HELLO_WORLD_NAME

What is the Dollar Sign?

We’ve seen the dollar sign in the last couple examples. This is a special character that does parameter expansion. In the case of our environment variables, when we printed out "Hello World, $HELLO_WORLD_NAME!”, it expanded to the value of our variable.

We can do the same with arguments to our shell script.

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