$ cat examples/intro/words.txt 
foo
foo
bar
foo
bar

$ grep bar examples/intro/words.txt 
bar
bar

$ grep -v bar examples/intro/words.txt 
foo
foo
foo

$ grep -n bar examples/intro/words.txt 
3:bar
5:bar

$ grep -n -v bar examples/intro/words.txt 
1:foo
2:foo
4:foo
