mkdir -p instead of mkdir

ln -sfn source target instead of ln -s source target

rm -f example.txt instead of rm example.txt

Modifying a file

if ! grep -qF "/mnt/dev" /etc/fstab; then
  echo "/dev/sda1 /mnt/dev ext4 defaults 0 0" | sudo tee -a /etc/fstab
fi

Check if variable, file or dir exists
formatting a device
mounting a device