正则表达式匹配非常特定的模式

Question

I have been trying to create a regex that would accept any of the values (SPAM, FOO, BAR) separated by a | or NONE. The regex I've been working on does the job, but a problem comes up when a value is entered before those values (See image below for more details). Any suggestions? Thank you!

^NONE$|^(?!. NONE)(?:. (FOO|BAR|SPAM))*

This is what I am currently working with.

Strings that should pass:

//Should Pass

FOO|BAR|SPAM

FOO

SPAM|BAR

SPAM|FOO

SPAM|FOO|BAR

BAR|FOO

NONE

//Should fail

NONE|FOO

FOO|SPAM|NONE

FOO|NONE|BAR ​ FOO|TEST

FOO_TEST

FOO TEST

FOO|TEST|BAR

FOO_TEST|BAR

​ TEST|FOO

TEST|FOO|BAR

TEST FOO|BAR

TEST_FOO|BAR

​ *TEST is being used as a word that is not in the group

Answer 1

这应该起作用： ^NONE$|^(FOO|BAR|SPAM)([|](FOO|BAR|SPAM))*$