# 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
```

![](/files/QLr0c8tpuPPKR7zwhTPH)

![](/files/vsCzzrSvYh4lErED3Fgx)

* **`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

![](/files/788neEb4ddtq1qLHwjeg)

* 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.

***


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://blog.syselement.com/tcm/courses/linux-101/6-shells/env-vars-files.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.