> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Work on the Command Line Part 2 Modify shell environment and variables

> Learn to view, customize, and persist environment variables on Linux, covering session tweaks, system settings, and automating tasks at login.

In this lesson, you’ll learn how to view, customize, and persist environment variables on Linux. We cover session-level tweaks, system-wide settings, and automating tasks at login.

## What Are Environment Variables?

Environment variables are key–value pairs that your shell and applications use to determine behavior, file locations, and settings. You can list all of them with either:

```bash theme={null}
printenv
env
```

Example output:

```bash theme={null}
$ env
PATH=/home/aaron/.local/bin:/home/aaron/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin
HISTSIZE=1000
GJS_DEBUG_TOPICS=JS ERROR;JS LOG
SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/2260,unix/unix:/tmp/.ICE-unix/2260
```

### Modifying Bash History Size

By default, `HISTSIZE=1000` limits your Bash history to 1 000 commands. To increase it for the current session:

```bash theme={null}
export HISTSIZE=2000
```

Verify:

```bash theme={null}
history
```

Sample:

```bash theme={null}
    1  sudo nano -w /etc/hosts
    2  ssh student@192.168.0.18
    3  ssh student@LFCS-CentOS2
    4  ls
    5  ls -laF
    6  cd .ssh
    7  ls
    8  nano -w known_hosts
    9  exit
   10  rm .ssh/known_hosts
```

## Common Environment Variables

Here are a few variables you’ll encounter frequently:

| Variable | Description                    | Example Usage    |
| -------- | ------------------------------ | ---------------- |
| HOME     | Current user’s home directory  | `echo $HOME`     |
| PWD      | Current working directory      | `echo $PWD`      |
| PATH     | Directories to search commands | `echo $PATH`     |
| HISTSIZE | Max number of history entries  | `echo $HISTSIZE` |

To display a variable’s value:

```bash theme={null}
echo $HOME
# /home/aaron
```

Use these expansions for platform-independent scripting:

```bash theme={null}
touch "$HOME/saved_file"
```

Each user running this command will create `saved_file` in their own home directory.

## Setting Persistent Environment Variables

User-specific variables can go in `~/.bashrc` or `~/.profile`, but for system-wide settings, use `/etc/environment`.

<Callout icon="lightbulb" color="#1CB2FE">
  Line-based syntax only—no shell expansions or functions.\
  Example entries look like `KEY="value"`.
</Callout>

### Edit `/etc/environment`

1. Open the file with root privileges:
   ```bash theme={null}
   sudo vim /etc/environment
   ```
2. Add your variable:
   ```bash theme={null}
   KODEKLOUD="https://kodekloud.com"
   ```
3. Save and exit.
4. Log out and back in, then verify:
   ```bash theme={null}
   echo $KODEKLOUD
   # https://kodekloud.com
   ```

<Callout icon="triangle-alert" color="#FF6B6B">
  Changes in `/etc/environment` affect all users and services.\
  Always back up `/etc/environment` before editing.
</Callout>

## Automating Commands on Login

To execute commands for every user at login, place shell scripts in `/etc/profile.d/`. For instance, record the last login time:

1. Create a script file:
   ```bash theme={null}
   sudo vim /etc/profile.d/lastlogin.sh
   ```
2. Add the following (no shebang required):
   ```bash theme={null}
   echo "Your last login was at:" > "$HOME/lastlogin"
   date >> "$HOME/lastlogin"
   ```
3. Save and exit.
4. Log out and back in, then check:
   ```bash theme={null}
   ls | grep lastlogin
   # lastlogin

   cat lastlogin
   # Your last login was at:
   # Thu Dec 16 10:42:37 UTC 2021
   ```

This script uses `$HOME` and demonstrates how to run tasks automatically upon user login.

***

## Links and References

* [Bash Reference Manual](https://www.gnu.org/software/bash/manual/)
* [Linux Environment Variables (TLDP)](https://tldp.org/LDP/abs/html/internalvariables.html)
* [Kubernetes Documentation](https://kubernetes.io/docs/)
* [Docker Hub](https://hub.docker.com/)

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