🐧 Linux Basics
Navigation
pwd # print working directory
cd # change directory
ls -l # list files in long format
ls -la # list all files including hidden files
cd .. # go up one directory
Files & Directories
cp
mv
rm -rf
mkdir
Processes
ps aux
top
kill -9
Permissions (ls -l)
ls -la # long list + hidden (.dot) files
# read the 10-char field: d rwx r-x r-x
# 1st char = type: - file, d directory, l link
# then 3 x rwx = owner / group / others
# r=read w=write x=execute (- = no permission)
-rw-r--r-- # file: owner read/write, others read-only
drwxr-xr-x # directory
-rwxr-x--- # has x = runnable program
drwx------ # only the owner can access (e.g. .ssh)
📝 Vim
Basic Commands
i # insert mode
esc # normal mode
:w # save
:q # quit
:wq # save and quit
Navigation
h j k l # move left, down, up, right
gg # go to top
G # go to bottom
💻 Shell
Basic Commands
echo "Hello, World!"
cat file.txt
grep "pattern" file.txt
Text Processing
cut -d: -f1 /etc/passwd # column 1 (: = delimiter, f = field)
grep -i "root" file # -i ignore case, -v invert, -n line numbers
sort file # sort lines
sort file | uniq -c # count duplicates (must sort first!)
sed 's/old/new/g' file # replace text (g = every match per line)
tr 'a-z' 'A-Z' < file # translate chars — reads stdin only, use <
tr -d '0-9' < file # delete chars
Pipes & Redirection
cmd1 | cmd2 # pipe: cmd1 output becomes cmd2 input
cmd > file # save stdout to file (overwrite)
cmd >> file # append to file
cmd < file # feed file in as stdin
cmd 2> err.txt # save stderr (errors) to file
cmd 2> /dev/null # throw errors away
cmd > out.txt 2>&1 # stdout AND stderr to same file
# stream numbers: 0 = stdin 1 = stdout 2 = stderr
Find & Count
find ~ -name "*.txt" # search recursively by name
find ~ -maxdepth 1 -name "*.txt" # top level only (don't go deep)
find ~ -size +1M # files bigger than 1 MB
find / -name "*.conf" 2> /dev/null # search all, hide permission errors
find ~ -name "*.txt" | wc -l # count matches (find + pipe + wc)
wc -l file # count lines (-w words, -c bytes)
🐍 Python
Basic Commands
python3 script.py
pip install package
uv venv
source .venv/bin/activate
deactivate
🗂 SQL
Basic Commands
SELECT * FROM table;
INSERT INTO table (col1, col2) VALUES (val1, val2);
UPDATE table SET col1 = val1 WHERE condition;
DELETE FROM table WHERE condition;
🌱 Git & GitHub
Local Git Basics
git init
git status
git add .
git commit -m "message"
git log --oneline
Branching
git branch
git branch new-branch
git checkout new-branch
git switch -c new-branch
git merge main
Remote Repositories (GitHub)
git remote -v
git remote add origin git@github.com:user/repo.git
git push -u origin main
git pull origin main
git fetch
Undo / Fix
git restore file.txt
git reset HEAD file.txt
git reset --soft HEAD~1
git reset --hard HEAD~1
GitHub Workflow
# clone a repo
git clone git@github.com:user/repo.git
# typical workflow
git pull
git add .
git commit -m "update"
git push
🌐 Networking
Basic Commands
ping
curl
nslookup
traceroute
IP & Interface
ip addr
ifconfig
netstat -tuln
SSH
ssh user@host
scp file user@host:/path
ssh-keygen
ssh-copy-id
Nginx
nginx -t
systemctl restart nginx
🐳 Docker
Basic Commands
docker build -t image_name .
docker run -d -p host_port:container_port image_name
docker ps
docker stop container_id
docker rm container_id
docker rmi image_id
☸️ Kubernetes
Basic Commands
kubectl get pods
kubectl get services
kubectl apply -f deployment.yaml
kubectl delete -f deployment.yaml
☁️ AWS
Basic Commands
aws s3 ls
aws ec2 describe-instances
aws lambda invoke --function-name my-function output.txt
aws cloudformation deploy --template-file template.yaml --stack-name my-stack