Ubuntu – How to watch the output that was filtered with grep

If you are just looking for a word you can use a for loop.

STRING="upgrade this if you can"
for x in $STRING; do
   echo $x
   if [ "$x" = 'upgrade' ]; then
       echo found
       y=$x
       break
   fi
done 
echo $y

If upgrade is always in the same position you could try array assignment.

declare -a z
z=($STRING)
echo ${z[0]}

If you want to use Perl regex syntax you need -P switch with grep. Check out previously asked guestion here Is grep syntax different from regex?