If you wanted to grab 10 lines from /var/log/messages, starting at the first line that has "pjungwlr" in it, you could:
$ less /var/log/msgs
/pjungwlr^M
^G (note line informational line numbers)
v (launch vi)
[double check your line #s, etc]
:d1,. (delete from 1st line, to current line)
10j (go down 10 lines)
:d,$ (delete to EOF)
:w my_newfile
:q