linux - Unbound variable during url printing in bash/shell -

I have 2 variables that I want to use to get a 3G variable:

  export REGION_NAME = phx export phx_url = https: //www.google.com  

I'm trying to do the following:

  The echo "$ (($ {REGION_NAME} _url})"  

and I get the following error:

  -sh: https: // www. Google.com: syntax error in expression (error token is "": //www.google.com ")  

All I'm trying to do I have to get one environment variable from each other but it does not work as easy as I think I will have to save it and nothing can be found online.

Thank you in advance for help. / P>

$ ((...)) is the arithmetic extension. It was not that try to expand the normal variable instead.

  REGION_NAME = phx phx_url = https: //www.google.com R_VAR = $ {REGION_NAME} _url "$ {! R_VAR} "echo