如何在脚本的持续时间内设置环境变量?

On Linux (Ubuntu 11.04) in bash, is it possible to temporarily set an environment variable that will only be different from the normal variable for the duration of the script? For example, in a shell script, making an app that saves to HOME portable by temporarily setting HOME to a folder in the present working directory, and then launching the app.On Linux (Ubuntu 11.04) in bash, is it possible