cd command doesn't work in my script
 

I dont know why, I wrote a script yesterday about select directory, then I find no matter what option I gave, I just wouldn't change directory.
So I wrote a script today which contains only one line.
and I just failed, with no error message. Any ideas?
Additional, I'm not at /home

It's about scope. when you run the script it invokes a new shell, and it's within that shell instances that you change directory. When you finish the script, that shell terminates, so nothing inside the shell persists to the parent it was executed from. If you want to run a list of commands in your current shell, you'd source the file. run ". myscript" and you'll change directory. the source dot there is broadly like an "include" statement in programming languages.

Then I find in a sub shell, pwd is still there, so Where can,I get to know the difference between bash and a sub shell.
I simply treat /bin/bash as a shell? Am I right?
Now I have some questions list here.
1:I invoke a sub ahell, where does this sub shell come from?
2:It's said that env variables is still supported in sub shell, why doesn't it have complete builtin command?
Thanks for your help.

http://www.tldp.org/LDP/Bash-Beginners-Guide/html/

BUT, I notice an Andy in your OS info

are you trying to write scripts for Android?

Ha,Just use phone to post.
Guess I'm really attached to my phone.

Bash is a shell (BASH -> Bourne Again SHell). The term bash shell is a pleonasm.

From the mother shell (the initial shell started when logging in). A mothewr shell can spawn child shells, which in turn can spawn child shells.

Maybe this might help clear things up a bit: Linux Shell environment