bash_automation_28-09-2021

## Special File Permissions (setuid, setgid and Sticky Bit)

find directory -user root -perm -4000 -exec ls -ldb {} \;

find / -user root -perm -4000 -exec ls -ldb {} \;

# Reference:
* https://docs.oracle.com/cd/E19683-01/816-4883/secfile-69/index.html
* https://docs.oracle.com/cd/E19683-01/816-4883/6mb2joatb/index.html

Every bash script starts with this string: “!#/bin/bash.” The exclamation point and hash symbol is known in the UNIX world as a “she-bang” and is the foundation of pretty much any UNIX-based script.



double ampersand (&&)? That tells the script to execute one command right after the other. 

It also tells the script to stop if something goes wrong. If you used a single ampersand, the script would continue even if the first command failed.


> sudo apt autoremove -y

libfprint-2-tod1 libllvm10
(Reading database ... 202619 files and directories currently installed.)


## Create a Shell Script to Install NGINX from Source On Ubuntu
https://aaronluna.dev/blog/install-nginx-source-code-shell-script/

https://medium.com/@ayeshasilvia/how-to-automate-interactive-installation-on-linux-short-sweet-ac59b345f84f

https://linuxhandbook.com/bash-automation/


https://code.tutsplus.com/tutorials/the-fundamentals-of-bash-scripting--net-32093

https://gist.github.com/sheikhwaqas/9088872

Reading database ... 202608 files and directories currently installed

sudo apt install silversearcher-ag

dpkg --list | wc --lines

find . -maxdepth 1 -type f | wc -l

I was curious to know which command actually causes this counting? The attempts I have made so far are:
https://askubuntu.com/questions/923425/aptitude-count-number-of-files-and-directories

ls -1 | wc -l

cat /var/lib/dpkg/info/*.list | sort | uniq | wc -l
202662

strings $(which dpkg) | grep "currently installed"

dpkg --listfiles hello

https://devconnected.com/how-to-count-files-in-directory-on-linux/


## How To Find Largest Top 10 Files and Directories On Linux / UNIX / BSD
https://www.cyberciti.biz/faq/how-do-i-find-the-largest-filesdirectories-on-a-linuxunixbsd-filesystem/

du -a /var | sort -n -r | head -n 10

sudo du /var/ -h --max-depth=999

Now, every command run in bash shell returns a value that’s stored in the bash variable “$?”. To get the value, run this command.


echo $?
If a command succeeded successfully, the return value will be 0. If the return value is otherwise, then it didn’t run as it’s supposed to


## single ampersand between 2 expressions
This is the bitwise AND operator.