echo value inside a variable ?

Question

x=102 y=x

means when i echo $y it gives x echo $y x --and not 102

and when i echo $x it give 102

lets say I dnt know what is inside y

and i want the value of x to be echoed with using y someting like this

a=`echo $(echo $y)`
echo $a

Ans 102

Answer 1

You need to tell the shell to evaluate your command twice -- once to turn $y into x, and again to get the value of $x. The most portable way I know to do this is with eval:

$ /bin/sh
$ x=100
$ y=x
$ echo $y
x
$ eval echo \$$y
100
$

(You need to escape the first $ in the eval line because otherwise the first evaluation will replace "$$" with the current pid)

If you're only concerned with bash, KennyTM's method is probably best.

Answer 2

In ksh 93 (I don't know whether this works in ksh 88):

$ x=102; typeset -n y=x
$ echo $x
102
$ echo $y
102
$ echo ${!y}
x

Confusingly, the last two commands do the opposite of what they do in Bash (which doesn't need to flag the variable using typeset).