The page will keep records of Linux commands which i think is helpful.
====== grep ======
  - ''grep "example" -i -n /etc/libuser.conf''
  - ''cat /etc/libuser.conf | grep "example" -i -n'' 
the command will find "example" in "/etc/libuser.conf" file and print it with line number

  - ''grep "imp" /etc/*.conf --color''
  - ''grep -i -r --include "*.bash" "domain" ./ --color''



====== find ======
  - ''find /etc -type f -maxdepth 1 -iname "*.conf"'' 

the command will find *.conf files without child directory in "/etc" directory
  - ''find /etc -type f -iname "*.conf" -exec grep "example" {} +
''
the command will find all "example" in all "*.conf" file in "/etc" directory and print the line

====== crontab ======
  - ''crontab -e''
to edit crontab tasks.

====== add user ======

  * adduser shaoxp
  * passwd shaoxp
  * gpasswd -a shaoxp wheel
    * or sudo adduser shaoxp sudo

above commands will finish add shaoxp as admin user.

====== awk ======
  * awk '{print $6 " " $1 " " $9}' ./file
  * awk '{print $6 " " $1 " " $9}' ./file| sort -n -r | more
  * cat file | awk -F ' ' '{if($1>10){print $1}}'  | wc -l