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--- linux:bash [2026/04/15 14:49] – [WILDCARD METACHARACTERS & EXPANSION] v1ctor
+++ linux:bash [2026/05/15 13:30] (current) – [REDIRECTS vs PIPES] v1ctor
@@ Line 7: / Line 7: @@
 Core wildcards:
   * * - zero or more characters. Example: ''ls *.jpg'' - all .jpg files in the current directory
-  * ? - exactly one character. Example: ''cp report?.pdf /backup/''   # report1.pdf, reportA.pdf, etc.
+  * ? - exactly one character. Example: ''cp report?.pdf /backup/'' - report1.pdf, reportA.pdf, etc.
+For example, following commands prints a list of files in the current directory:
+<code bash>
+$ echo *
+</code>
+What's happening:
+  - Globbing (before echo runs) - The shell — not echo — expands * by looking at the current directory and replacing * with a space-separated list of matching filenames.
+**Disabling expansion**
+  * If you don’t want the shell to expand a glob in a command, enclose the glob in single quotes (' '). For example, the command echo '*' prints a star.
+  * This might be useful when running commands like ''find'', to pass patterns containing wildcards
+  * The reason why ''find'' works sometimes is because shell expansion only happens if matches exist in the current directory
 ==== HERE DOCUMENTS ====
@@ Line 36: / Line 49: @@
 </code>
-==== FILESYSTEM ====
+==== ENVIRONMENT VARIABLEs ====
+Environment variables are named values stored by the shell/OS that processes can read to configure their behavior. Think of them as a key-value store available to every running program.
+Environment variables are **not** global system state. They are per-process (and inherited downward only).
+Setting an env variable for the current session:
+<code bash>
+export STUFF=blah
+</code>
+To make env variable permanent, you need to store it in a file. Which file - depends on the Shell type:
+Type of Shells:
+^ Shell Type ^ When it starts ^ Example ^ Reads file ^
+| Login Shell | You authenticate (SSH, TTY login, su -, bash -l) | SSH into a server | ~/.profile |
+| Interactive non-login | You open a new terminal in an existing session | New tab in your terminal  emulator | ~/.bashrc |
+  * **~/.profile** — runs once per login session. Good for:
+    * export PATH=..., export EDITOR=vim
+  * **~/.bashrc** — runs every time you open a new interactive bash shell. Good for:
+    * aliases, shell functions, prompt
+==== REDIRECTS vs PIPES ====
+The core difference: redirects connect a stream to a file (a redirect always has a file on one side). Pipes connect one process to another process.
+Pipes: process → process:
+<code bash>
+cmd1 | cmd2           # Takes cmd1's stdout and feeds it directly into cmd2's stdin. No file involved
+ls | grep ".txt"      # ls output becomes grep's input
+</code>
+==== STANDARD INPUT and OUTPUT ====
+Unix programs have 1 input and 2 outputs.
+When you run a command from a terminal, they all go to/from the terminal by default, e.g.:
+<code bash>
+$ cat
+hello   # Stdin is connected to the terminal, you can type there.
+hello   # Stdout - cat prints it right away after you pressed enter.
+</code>
+** < redirects Stdin**
 <code bash>
-stat file.txt            # shows additional details of the file (when created/modified etc)
+cat < foo.txt
+bar
 </code>