🧭 1️⃣ What Is Bash?

Bash = Bourne Again Shell 

(the command-line interface for Linux & macOS)

Why learn it?

Automate tasks

Manage files & servers

Understand what GUIs hide

💡 Try it:

echo "Welcome to Bash!"
whoami

📂 2️⃣ Getting Your Context

Commands:

pwd        # show current directory
ls         # list files
ls -la     # long + hidden
cd /tmp    # change directory
cd ..      # go up one level
cd ~       # go home


🧠 Exercise:
Navigate to /tmp, list all files, then return to your home.

🧱 3️⃣ Create / Modify / Delete Files & Folders

Basic commands:

mkdir testdir
cd testdir
touch hello.txt
echo "Hello Bash" > hello.txt
cat hello.txt
cp hello.txt copy.txt
mv copy.txt renamed.txt
rm renamed.txt
rmdir emptydir


🧠 Exercise:
Create a folder, write a message to a file, then delete both.

🔗 4️⃣ Pipelines & Filters

Connect commands with | (pipe).

Examples:

echo -e "apple\nbanana\napple\norange" > fruits.txt
cat fruits.txt | grep apple
cat fruits.txt | grep -v banana
cat fruits.txt | wc -l
ls /bin | grep bash | head -5


🧠 Exercise:
Count how many .sh files exist in /usr/bin:

ls /usr/bin | grep '\.sh$' | wc -l

🧮 5️⃣ Variables & Data Representation

Set and use variables:

NAME="Alice"
echo "Hello $NAME"


Random numbers:

echo $RANDOM
echo $((RANDOM % 10))


Convert data formats:

printf "%d\n" 0xFF    # hex → decimal
printf "%x\n" 255     # decimal → hex
printf "%d\n" "'A"    # ASCII → decimal


🧠 Exercise:
Generate a random number between 1–100 and print it in hex:

N=$((RANDOM % 100 + 1)); printf "%x\n" $N

✍️ 6️⃣ Saving & Editing Files (vim)

vim is a powerful terminal text editor.

Start editing:

vim notes.txt


Modes:

i → Insert mode (start typing)

Esc → Command mode

Exit commands:

:wq → Save & quit

:q! → Quit without saving

🧠 Exercise:
Open notes.txt, write one line, save it, and check with cat.

🧩 7️⃣ Summary

✅ Navigation → pwd, ls, cd
✅ Files → touch, mkdir, rm, cat
✅ Pipelines → |, grep, wc
✅ Variables → $VAR, $RANDOM, printf
✅ Editing → vim :wq





💡 Try combining them:

echo $RANDOM > numbers.txt
cat numbers.txt | wc -c

🏁 Extra Challenges

Use history | tail -5 to review last commands





Create your first script:

#!/usr/bin/env bash
echo "Hello, $(whoami)!"


Then:

chmod +x hello.sh
./hello.sh