cd /var/log          # absolute path
cd src/components    # relative path
cd ..                # parent directory
cd ~                 # home directory
cd -                 # previous directory

ls                   # basic listing
ls -la               # long format + hidden files
ls -lh               # human-readable sizes
ls -lt               # sort by modification time
ls -lS               # sort by size
ls *.js              # glob pattern

pwd
# /home/user/projects/my-app

cp file.txt backup.txt          # copy file
cp -r src/ src-backup/          # copy directory recursively
cp -i file.txt dest/            # prompt before overwrite
cp file1.txt file2.txt dest/    # copy multiple files

mv old.txt new.txt              # rename
mv file.txt ~/Documents/        # move to directory
mv -i src.txt dest.txt          # prompt before overwrite

rm file.txt                     # delete file
rm -r directory/                # delete directory recursively
rm -i file.txt                  # prompt before delete
rm -f file.txt                  # force (no prompt)

mkdir new-folder                # create directory
mkdir -p a/b/c                  # create nested directories
touch file.txt                  # create empty file (or update timestamp)

cat file.txt                    # print entire file
head -n 20 file.txt             # first 20 lines
tail -n 20 file.txt             # last 20 lines
tail -f /var/log/app.log        # follow log in real time
less file.txt                   # scrollable viewer (q to quit)

chmod 755 script.sh             # rwxr-xr-x
chmod 644 file.txt              # rw-r--r--
chmod +x script.sh              # add execute
chmod -w file.txt               # remove write
chmod u+x,g+r file.txt         # user +exec, group +read

# Permission numbers:
# r=4  w=2  x=1
# 7 = rwx, 6 = rw-, 5 = r-x, 4 = r--
# First digit: owner, second: group, third: others

chown user file.txt             # change owner
chown user:group file.txt       # change owner and group
chown -R user:group directory/  # recursive

find . -name "*.js"                    # by name
find . -type f -name "*.log"           # files only
find . -type d -name "node_modules"    # directories only
find . -size +10M                      # larger than 10MB
find . -mtime -7                       # modified in last 7 days
find . -name "*.tmp" -delete           # find and delete

grep "error" log.txt                   # search in file
grep -r "TODO" src/                    # recursive search
grep -i "hello" file.txt               # case-insensitive
grep -n "function" app.js              # show line numbers
grep -l "import" src/*.ts              # list matching files only
grep -c "error" log.txt               # count matches
grep -E "error|warning" log.txt        # regex (extended)

ps aux                          # all processes
ps aux | grep node              # filter by name
ps -ef --forest                 # tree view

top                             # built-in monitor
htop                            # better UI (install separately)
# Press q to quit, k to kill a process

kill 1234                       # graceful stop (SIGTERM)
kill -9 1234                    # force kill (SIGKILL)
killall node                    # kill all by name
pkill -f "node server.js"      # kill by pattern

curl https://api.example.com              # GET
curl -o file.zip https://example.com/f.zip # download
curl -X POST -H "Content-Type: application/json" \
  -d '{"name":"Alice"}' https://api.example.com/users
curl -I https://example.com               # headers only
curl -s https://api.example.com | jq .    # pipe to jq

wget https://example.com/file.zip
wget -O output.zip https://example.com/file.zip
wget -q https://example.com/file.zip     # quiet mode

# SSH
ssh user@hostname
ssh -p 2222 user@hostname                # custom port
ssh -i ~/.ssh/key.pem user@hostname      # with key
SCP (secure copy)
scp file.txt user@host:/path/            # upload
scp user@host:/path/file.txt ./          # download
scp -r folder/ user@host:/path/          # directory

# Create .tar.gz
tar -czf archive.tar.gz folder/
Extract .tar.gz
tar -xzf archive.tar.gz
List contents
tar -tzf archive.tar.gz
Extract to specific directory
tar -xzf archive.tar.gz -C /dest/

zip archive.zip file1.txt file2.txt
zip -r archive.zip folder/
unzip archive.zip
unzip archive.zip -d /dest/
unzip -l archive.zip              # list contents

sudo apt update                  # update package list
sudo apt upgrade                 # upgrade all packages
sudo apt install nginx           # install package
sudo apt remove nginx            # remove package
apt search keyword               # search packages
apt list --installed             # list installed

brew install node                # install
brew uninstall node              # remove
brew update                      # update Homebrew
brew upgrade                     # upgrade all packages
brew list                        # list installed
brew search keyword              # search

# Pipe output to another command
cat log.txt | grep "error" | wc -l
Redirect output to file (overwrite)
echo “hello” > file.txt
Append to file
echo “world” >> file.txt
Redirect stderr
command 2> errors.log
Redirect both stdout and stderr
command > output.log 2>&1
Input from file
sort < unsorted.txt

# Delete all .tmp files
find . -name "*.tmp" | xargs rm
Run command for each line
cat urls.txt | xargs -I {} curl {}
Parallel execution
find . -name “*.jpg” | xargs -P 4 -I {} convert {} {}.png