Linux and Shell Scripting

 Nice article on firewalls: here

$? -> It will give last executed command exit code, any non zero number idicates failure and zero means success. For example: If we try to remove a file which is not present using rm,they it will say no such directory or file and in the next command if we use '$?' it will return 1 or any number except zero !<CMD>  -> It executes the last executed command i.e !ls means last excuted ls..The most common use case of this is if we want to execute a large command we can get the history number of the same using history and use !<history number>  For example: If we want to execute ansible playbook using $anisble playbook <playbook_name> -i <inventory file location> --vault-password-file=./vault_pass , then we need to use above lenghty command repeatedly, instead of that get the history numer using $history and use that number with $!<history number>  , it will invoke this lengthy command groups -> This command is used to list all the groups...

 RHCSA(Redhat Certified System Administrator) : drive link Tech Arkith Linux and Bash scripting notes: click here Devops Learn Easy youtube, Linux Administartion Play List: here Devops Learn Easy youtube, Bash Scripting Play List: here