command_to_run | grep text_to_find
command_to_run | more
command_to_runfile_to_write_ouput.txt
less abc.txt
vim abc.txt
tail -f abc.txt
head abc.txt
cat abc.txt
grep text_to_search -rniH .
### :Managing files
ls
ls -al
ln -s abc def
chown some_user_name:some_group_name -R *
chmod +x command_to_run _later.sh
rm
rm -rf folder_name_to_delete_recursively_and_dangerously
rmdir folder_name_to_delete
touch filename
tar cvzf abc.tgz source_folder_name_or_Filename
tar xvzf abc.tgz
ps -ef
netstat -an
sudo command_to_run
su
su -
wget http://www.abc.co.kr/file_to_download.txt
history
df -h
mount -l
ifconfig
ping google.com
export
export ABC=DEF
echo
top
service network restart
source env_file_to_run