How to add a variable to the the existed environment variable in a bash command

How to add a variable to the the existed environment variable in a bash command:

1. Let's suppose that you already have a some env.variable (check all variables that you have with command env). As an example we'll use REPO_B

2. Say you want to run svn check out from the branch repository and do check out the specific branch branchA.

3. The syntaxys is like this:
svn co REPO_B/branchA branchA

If you're a developer and have an iPad

If you're a developer and have an iPad sheck this link:
http://omz-software.com/editorial/