# Environment variables

## What is it?

On the linux system we technically have 2 variables **Environment** and **Shell**

### Environment variables

An **environment variable** is a special kind of variable that is **copied from the system into a process** when it starts. It lives as a **process-wide variable** inside that process.

### Shell variables

used in shell scripts for many functionalities like storing data and information, taking input from users, printing values that are stored

## Viewing and modifying

To view or modify the environment variables we use `env`

You will see some uppercase strings like HOME, PATH, SHELL and etc. Those are default environment variables

### view ALL variables

Use `set` to view all variables you can do with `more` or `less`

### Changing variables

To change variables simply type the parameter and the value in your terminal

```bash
$ set | grep HISTSIZE #HISTSIZE is storing the past commands and change to 0 makes it store nothing
  HISTSIZE=1000
$ HISTSIZE=0
$ set | grep HISTSIZE
  HISTSIZE=0
```

**Make it permanent**

`export` is which make things permanent

save the original first :)

```bash
$ echo $HISTSIZE > ~/OrgvalueofHISTSIZE.txt #save the original value
$ set > ~/savedvalues.txt #saves all original values
```

```bash
$ HISTSIZE=0
$ export HISTSIZE #and then it will be permanet
```

## Cool variables

### PS1

Set the shell prompt as you need

* `\u` The name of the current user
* `\h` The hostname
* `\w` The base name of the current working directory

```bash
┌──(vix㉿D3sKt0P-90000)-[~]
└─$ PS1="My Shell $"

My Shell $
My Shell$PS1='\uก็็\h|\w $'

vixก็็D3sKt0P-90000|~ $cd Music
vixก็็D3sKt0P-90000|~/Music $
```

### PATH

This is the one of most important variables

Most of the commands stored in **sbin** or **bin** files so that if you type `ls` , `cd` and things like that will work

```bash
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
```

This will be really useful when installing new tools, let’s say you downloaded a cool tool from github and every time you need to go to the directory in order to use it, so why not add it to PATH

**DO NOT DO THINGS LIKE:** ~~`$ PATH=/root/cooltool`~~ it will replace all of the paths inside

```bash
$ PATH=$PATH:/root/cooltool
$ echo $PATH
/usr/local/sbin:usr/local/bin:/usr/sbin:/sbin/bin:/root/cooltool
```

### Define your own variable

```bash
$ MYVARIABLE="Hello still learning"
$ echo $MYVARIABLE
Hello still learning

$ unset  MYVARIABLE #to clear/unset the value of the variable
$ echo $MYVARIABLE
#blank
```


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