You could use escaping to latex to emphasize the intended lines.
Check out Chapter 4.14 Escaping to LATEX of the Listings package manual.
Or, you could refer to certain line numbers.
Check out Chapter 7 How to's
This is some code of mine: i searched for all running processes on my machine and fed the output to grep. grep then searched for the pattern 'Foam'. I marked all matches red in the listing.
\begin{lstlisting}[escapechar=§,caption={In der Liste der laufenden Prozesse suchen},label=lst:listProcessesFindFoam]
user@host:~$ ps -ef | grep Foam
user 11005 5117 0 17:11 pts/2 00:00:05 mpirun -np 4 twoPhaseEuler§\color{red}{Foam}§ -parallel
user 11006 11005 99 17:11 pts/2 00:40:27 twoPhaseEuler§\color{red}{Foam}§ -parallel
user 11007 11005 99 17:11 pts/2 00:40:28 twoPhaseEuler§\color{red}{Foam}§ -parallel
user 11008 11005 99 17:11 pts/2 00:40:27 twoPhaseEuler§\color{red}{Foam}§ -parallel
user 11009 11005 99 17:11 pts/2 00:40:26 twoPhaseEuler§\color{red}{Foam}§ -parallel
user 11673 11116 0 17:52 pts/12 00:00:00 grep --color=auto §\color{red}{Foam}§
user 32041 1 0 Aug01 ? 00:00:31 evince /tmp/lyx_tmpdir.J18462/lyx_tmpbuf0/open§\color{red}{Foam}§UserManual_CDLv2.pdf
user@host:~$
\end{lstlisting}