($txt = 'arvec') =~ /(ar|ec|vec)$/

1. ^arvec  - check for ar$  -> fail (because of the end-of-string anchor)
           - check for ec$  -> fail
           - check for vec$ -> fail

2. a^rvec  - check for ar$  -> fail
           - check for ec$  -> fail
           - check for vec$ -> fail

3. ar^vec  - check for ar$  -> fail
           - check for ec$  -> fail
           - check for vec$ -> success, $1 becomes 'vec'