adding 03 understanding env notes (#12)

weekly_lessons/03-env/README.md

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+# Week 03 ( understanding your env )
+
+- [Week 03 ( understanding your env )](#week-03--understanding-your-env-)
+  - [Pre-reqs](#pre-reqs)
+  - [Why](#why)
+  - [Examples](#examples)
+  - [Resources](#resources)
+
+## Pre-reqs
+
+- bash setup
+  - [video](https://youtu.be/mfP8R1yr80A)
+  - [writen instruction](/install_methods/)
+
+## Why
+
+1. can affect how you terminal responds to commands
+2. possibly used maliciously (i.e. EDITOR) ( Itzik Kotler )
+
+    [![BACE YT image](https://i.ytimg.com/vi/vMxEKjx0UEk/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLCVgd230LQ4-q6BrZ2yPCRg_9-w_A)](https://youtu.be/oO2Df7Y6ywY)
+
+3. know what your working with in a pentest
+      - possibly contextual environment variables
+      - possibly credentials if service account
+      - context for privlege currently running under
+      - possible attack paths for PATH variable
+      - SSH key attack ( Hal Pomeranz )
+
+        [![youtube preview pic](https://i.ytimg.com/vi/-jNkjuWMFrk/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLAB_c5Hehtcu85yasZg3BsgvISLMA)](https://youtu.be/-jNkjuWMFrk?t=1840)
+
+## Examples
+
+```bash
+type env
+env
+type set
+help set | less
+set | less
+testingz(){
+  echo hello
+}
+set
+exit
+set
+pe-bash
+set | grep SHELL
+sh
+help
+set
+```
+
+## Resources
+
+- [cd man page](https://ss64.com/bash/cd.html)
+- [modified hardend scripting env](https://elrey.casa/bash/scripting/harden)