Try this one :
(?<=SAT)(.+?)(?=SAT)
What it actually does is look behind and forward for SAT
.
If you want to test per string and use the whole string as the sample, then just use this modified version : ^(?<=SAT)(.+?)(?=SAT)$
Btw, just tried this one out (SAT([^(SAT)]+)SAT
) and it seems to be working too. Here's a demo : http://regex101.com/r/fJ4gO5