如何在bash脚本中使用正则表达式否定测试?

Using GNU bash (version 4.0.35(1)-release (x86_64-suse-linux-gnu), I would like to negate a test with Regular Expressions. For example, I would like to conditionally add a path to the PATH variable, if the path is not already there, as in:Using GNU bash (version 4.0.35(1)-release (x86_