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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 ``` # Persistent Environment variables ### **Files that affect behavior of every user:** * _**/etc/bash.bashrc**_: This file is read whenever an interactive shell is started (normal terminal) and all the commands specified in here are executed. * _**/etc/profile and /etc/profile.d/\***_**:** This file is read every time a user logs in. Thus all the commands executed in here will execute only once at the time of user logging in. * **Example: ** `/etc/profile.d/somescript.sh` ```bash #!/bin/bash TEST=$(cat /var/somefile) export $TEST ``` ### **Files that affect behavior for only a specific user:** * _**\~/.bashrc**_: This file behaves the same way _/etc/bash.bashrc_ file works but it is executed only for a specific user. If you want to create an environment for yourself go ahead and modify or create this file in your home directory. * _**\~/.profile, \~/.bash\_profile, \~/.bash\_login**_**:** These files are same as _/etc/profile_. The difference comes in the way it is executed. This file is executed only when a user in whose home directory this file exists, logs in. **Extracted from:** [**here**](https://codeburst.io/linux-environment-variables-53cea0245dc9) **and** [**here**](https://www.gnu.org/software/bash/manual/html\_node/Bash-Startup-Files.html) # Common variables From: [https://geek-university.com/linux/common-environment-variables/](https://geek-university.com/linux/common-environment-variables/) * **DISPLAY** – the display used by **X**. This variable is usually set to **:0.0**, which means the first display on the current computer. * **EDITOR** – the user’s preferred text editor. * **HISTFILESIZE** – the maximum number of lines contained in the history file. * **HISTSIZE - **Number of lines added to the history file when the user finish his session * **HOME** – your home directory. * **HOSTNAME** – the hostname of the computer. * **LANG** – your current language. * **MAIL** – the location of the user’s mail spool. Usually **/var/spool/mail/USER**. * **MANPATH** – the list of directories to search for manual pages. * **OSTYPE** – the type of operating system. * **PS1** – the default prompt in bash. * **PATH - **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** – the current working directory. * **SHELL** – the path to the current command shell (for example, **/bin/bash**). * **TERM** – the current terminal type (for example, **xterm**). * **TZ** – your time zone. * **USER** – 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 The processes will use the **proxy** declared here to connect to internet through **http**. ```bash export http_proxy="http://10.10.10.10:8080" ``` ## https\_proxy The processes will use the **proxy** declared here to connect to internet through **https**. ```bash export https_proxy="http://10.10.10.10:8080" ``` ## PS1 Change how your prompt looks. **I have created **[**this one**](https://gist.github.com/carlospolop/43f7cd50f3deea972439af3222b68808) (based on another, read the code). 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>)

Support HackTricks and get benefits!

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