General
Check exit code of previous command (0 = success, 1 = error)
echo $?
File & Directory Management
List files with details
ls -la
Show current directory
pwd
Create directory
mkdir foldername
Remove file
rm filename
Remove directory recursively
rm -r folder
Search & Filtering
Search for text inside files
grep -R "text" .
Search for files by name
find . -name "*.js"
Search command history
history | grep keyword
Permissions & Ownership
Change file permissions
chmod 755 file
Change owner and group
chown user:group file
Networking
Test connectivity
ping google.com
Check open ports
ss -tulpn
Download file
curl -O https://example.com/file
Compression
Extract .tar.gz archive
tar -xzvf archive.tar.gz
Create .tar.gz archive
tar -czvf archive.tar.gz folder/
Process Management
List running processes
ps aux
Kill a process
kill PID
Force kill a process
kill -9 PID