i have been given an assignment by my teacher to write my own commands using Linux shell,can anyone guide me regarding this problem?

First a piece of advice: if you don't understand your homework you should always ask your teacher for guidance! You should never be afraid of asking your teacher for help. Your teacher decides what you should learn while taking a course and while I (and many others) are happy to help: it's still your teacher who decides what you need to know to pass the course! We might teach you great stuff, but if you're unlucky none of it will come on your test.

With that said, maybe you should read this:
linuxcommand.org/learning_the_shell.php

Good luck!

Hi,

welcome to Linux questions.

For one of the best introductions to using a machine running GNU/Linux please have a (good) look at:

http://rute.2038bug.com/index.html.gz

If you have further questions (you must have!) please let us know.

Cheers,

Evo2.

PS. Many others will suggest other good refs.