> For the complete documentation index, see [llms.txt](https://blog.syselement.com/tcm/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://blog.syselement.com/tcm/courses/linux-101/6-shells/env-vars-files.md).

# Environment Variables & Startup Files

## Environment Variables

* The shell stores information in the environment variables.
* Each shell has its own values for these variables.

### printenv

```bash
printenv
# Prints name and value pairs for all the environment variables
# VARIABLE_NAME=VALUE

printenv | grep PATH
```

![](https://1178537843-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F2KUxfxUFmy000PDT7MtM%2Fuploads%2Fgit-blob-8b4652a44fe91bb4fe59741facc6ca618afba600%2Fimage-20221010190521527.png?alt=media)

![](https://1178537843-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F2KUxfxUFmy000PDT7MtM%2Fuploads%2Fgit-blob-c436c78acefebb7957d45d1eaf9856f28a01cfae%2Fimage-20221010191004310.png?alt=media)

* **`SHELL`** - user's shell is bash
* **`PWD`** - current working directory
* **`HOME`** - home directory for the current user
* **`PATH`** - list of the directories searched in order, to find commands to be executed.
  * Current working directory can be put first in this path, easier to execute current working directory programs but can be used for attacks.

There are two types of environment variables: **global** and **local**.

## Global

* **Global** variables can be accessed by anything executed in that shell = `Environment Variables`

### export / unset

```bash
# Create a global variable
export COUNT_GLOBAL=33
echo $COUNT_GLOBAL
	33

# Unset a variable
unset COUNT_GLOBAL
```

## Local

* **Local** variables are valid only for the current shell (and not for sub-shells) = `Shell Variables`

```bash
# Create a shell variable
COUNT_LOCAL=42
echo $COUNT_LOCAL
	42
# $ is used to tell the shell that it is a variable

# Change shell (create sub-shell) and check the variable doesn't exist
bash
echo $COUNT_LOCAL
```

## Startup files

* When starting a new bash shell, the shell is configured using startup files.
* Interactive non-login shell - the type of shell opened by the Terminal

```bash
nano .bashrc
# There are various configurations for the shell and commands aliases
# Aliases can be added at the bottom of this file
```

* `alias name='COMMAND_VALUE'` - the alias uses the entire command enclosed in single quotes

![](https://1178537843-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F2KUxfxUFmy000PDT7MtM%2Fuploads%2Fgit-blob-6fa082b9b720443fbe9b3b7a4aa86d352ee84800%2Fimage-20221010203032874.png?alt=media)

* After adding an alias, a new shell must be created to make the alias work, or use the **`source .bashrc`** command in the same shell.

```bash
source .bashrc
# Re-runs all the commands in the .bashrc file in the current shell
```

* Using a shell other than bash, the startup file name will be different.

***