Look into bash builtin command named typeset

$typeset -n gree=55
bash: typeset: 55': invalid variable name for name reference
$typeset -n 55=gree
bash: typeset:55=gree': not a valid identifier
$typeset -n gree=pwd
$echo $gree

$echo $pwd

$typeset -n vary=$?
bash: typeset: `0': invalid variable name for name reference
$typeset vary=$?
$echo $vary
1
$echo $vary
1
$echo $?
0
$echo $vary
1
$echo vary
vary
$echo $vary
1
$echo $vary
1
$echo $?
0
$typeset vary=$?
$echo $vary
0
$

$typeset hello
$echo $hello

$echo $?
0
$typeset hello
$echo $?
0
$typeset -r hello=1
$typeset hello=2
bash: typeset: hello: readonly variable
$

http://tldp.org/LDP/abs/html/declareref.html