# Linux Environment Variables
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***
## Global variables
The global variables **will be** inherited by **child processes**.
You can create a global variable for your current session doing:
```bash
export MYGLOBAL="hello world"
echo $MYGLOBAL #Prints: hello world
```
This variable will be accessible by your current sessions and its child processes.
You can **remove** a variable doing:
```bash
unset MYGLOBAL
```
## Local variables
The **local variables** can only be **accessed** by the **current shell/script**.
```bash
LOCAL="my local"
echo $LOCAL
unset LOCAL
```
## List current variables
```bash
set
env
printenv
cat /proc/$$/environ
cat /proc/`python -c "import os; print(os.getppid())"`/environ
```
## Common variables
From: [https://geek-university.com/linux/common-environment-variables/](https://geek-university.com/linux/common-environment-variables/)
* **DISPLAY** β the display used by **X**. This variable is usually set to **:0.0**, which means the first display on the current computer.
* **EDITOR** β the userβs preferred text editor.
* **HISTFILESIZE** β the maximum number of lines contained in the history file.
* **HISTSIZE** β Number of lines added to the history file when the user finish his session
* **HOME** β your home directory.
* **HOSTNAME** β the hostname of the computer.
* **LANG** β your current language.
* **MAIL** β the location of the userβs mail spool. Usually **/var/spool/mail/USER**.
* **MANPATH** β the list of directories to search for manual pages.
* **OSTYPE** β the type of operating system.
* **PS1** β the default prompt in bash.
* **PATH** β stores the path of all the directories which holds binary files you want to execute just by specifying the name of the file and not by relative or absolute path.
* **PWD** β the current working directory.
* **SHELL** β the path to the current command shell (for example, **/bin/bash**).
* **TERM** β the current terminal type (for example, **xterm**).
* **TZ** β your time zone.
* **USER** β your current username.
## Interesting variables for hacking
### **HISTFILESIZE**
Change the **value of this variable to 0**, so when you **end your session** the **history file** (\~/.bash\_history) **will be deleted**.
```bash
export HISTFILESIZE=0
```
### **HISTSIZE**
Change the **value of this variable to 0**, so when you **end your session** any command will be added to the **history file** (\~/.bash\_history).
```bash
export HISTSIZE=0
```
### http\_proxy & https\_proxy
The processes will use the **proxy** declared here to connect to internet through **http or https**.
```bash
export http_proxy="http://10.10.10.10:8080"
export https_proxy="http://10.10.10.10:8080"
```
### SSL\_CERT\_FILE & SSL\_CERT\_DIR
The processes will trust the certificates indicated in **these env variables**.
```bash
export SSL_CERT_FILE=/path/to/ca-bundle.pem
export SSL_CERT_DIR=/path/to/ca-certificates
```
### PS1
Change how your prompt looks.
[**This is an example**](https://gist.github.com/carlospolop/43f7cd50f3deea972439af3222b68808)
Root:
.png>)
Regular user:
.png>)
One, two and three backgrounded jobs:
.png>)
One background job, one stopped and last command didn't finish correctly:
.png>)
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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