Test 1
Test 2
Test 3
Test 4
UNIX
Test 5
Test 6
Test 7
Test 8
Test 9

Test 5
Test 6

$ awk '$0 == "UNIX" {i=1;next};i && i++ <= 2' file
Test 5
Test 6

grep -A2 -P '^UNIX$' file

awk '$0=="UNIX"{getline; print; getline; print}' file

sed -n '/^UNIX$/{n;p;n;p}' file

grep -A 2 UNIX file.txt

-A NUM, --after-context=NUM
      Print NUM  lines  of  trailing  context  after  matching  lines.
      Places  a  line  containing  --  between  contiguous  groups  of
      matches.

sed -n '/UNIX/{n;p;n;p}' /path/to/file

$ for i in {1..9}; do echo $i; done | sed -n '/4/{n;p;n;p}'
5
6

ex -s +'1,/UNIX/d|%p|q!' file_or_/dev/stdin