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