egrep - extends grep to handle ranges [2]
egrep -n 'Lab(oratorie)?s' ch04.txt to find lines that have either “Labs” or “Laboratories” and display those lines with their line numbers
2:AT&T Unix Wisdom by AT&T Labs
11:--by AT&T Laboratories -- original makers of UNIX
? Means match 0 or 1 of “oratorie”