Normally i would do this-

cd abc
ls -ltr

I wish to run above command in a single line, like this-

cd abc | ls -ltr

But above command doesn't works, it simply runs the second command, ignoring the 1st one.

Replace the pipe (|) with a semicolon like this:

cd dir-name; ls -lrt

This is so cool. Thanks

Does this means I am not innovative or dumb...I know how to script...why this stuff did not come to my mind?

There is a one way to know, can you tell me how did you first come to know about this? I've read unix books, but none talk like this at command level.

A better way is to list the directory contents only if it exists and is readable:

cd dir-name && ls -lrt

Some of these kinds of things come with time, and experience and through asking questions as you did. Hard to say when I first learned something like this. The one thing that I do know is that I tend to learn something new with nearly every question that I answer. This turns out to be no exception when looking at jlliagre's post -- I tend to think in traditional if-then-else constructs when I depend on successful command execution and thus don't think about the command && command style one liners which as pointed out is better than simply banging two commands onto one line.