Hi everyone,

I'm looking for resources to learn Linux shell commands and writing custom shell in Linux. Please guide me.

first of all you have most probably an installed linux somewhere, this is the most important resource you can use.
You can go to www.tldp.org to learn. for example http://tldp.org/LDP/Bash-Beginners-Guide/html/.
I do not really understand what do you mean by "writing custom shell".

In addition to the above guidance, these three are very helpful for learning shell scripting:

https://mywiki.wooledge.org/BashPitfalls
https://mywiki.wooledge.org/BashGuide
https://mywiki.wooledge.org/BashFAQ

However, it helps not to think of programs as "commands" that you learn in advance but to recognize them as a collection of useful utilities which each do one thing well. And as such you can approach it from a programming perspective and learn them just-in-time as needed. If you do that, then it is useful to learn to navigate the system and be able to find the right tool for any given task.

You can see all the utilities that are installed on your system using apropos by searching all manual pages from sections 1, 5, and 8:

Towards the bottom of the manual pages, there is also a "See Also" section which is often quite helpful when looking for the right utility. Also, keep in mind that the manual pages are reference manuals not tutorials or guides. Look to the Web for guides or tutorials, or ask here. The manual pages do vary in quality though and while some are very, very good some are less so.

I assume the guy asks about shell script. But these are usually limited to one shell you choose.

When you want to learn bash. You should use a distro which focus on customisation like gentoo. I would not use mint / fedora and such. When you have to do basic tasks in a shell regularly when you update your box, your knowledge will increase over the time. when you use graphical user interfaces it will not.

"The Linux Command Line", download the pdf, or buy the book.
http://linuxcommand.org/tlcl.php

Here's a student's tutorial
http://www.ee.surrey.ac.uk/Teaching/Unix/
This is also handy
http://mywiki.wooledge.org/BashGuide

Be patient with yourself and don't try to learn too fast!

You can download 'The Linux Command Line' book in PDF format here.

No, (s)he just posted some windows related links to payware...

https://www.linuxquestions.org/quest...5/#post5852727