How to make shell variable don't expand immediately
 

assumption:
X=/home/user
Y=${X}/tmp

When the X variable is changed,However the Y variable isn't changed according to X's change,Y already expand when define it.

Is there any way that expand variable when only referring Y variable ,not define it?

Thanks

Uhm.. this is not called expanding I believe. Expanding is when file* becomes file1 file2 file34 etc. IMHO.

As for your problem, Y get the value of $X when you say it has to get it, i.e. Y=$X gives the value of $X to Y, and no matter what happens to X afterwards, Y won't change. It is one of the fundamentals of programming in this type of languages.

In an ordinary programming language you would create a function getY or so which would look at $X at the moment of calling. But Bash doesn't provide function return values, at least not easily.

The only thing you can do is NOT using Y, but always ${X}/tmp when you need this string. You can beautify your program a bit more to define /tmp just once Z="/tmp", so if you have to change this value you'd only have to do it in one place. You reference would become: ${X}/${Z} wherever you use $Y now.

jlinkels