These examples show how grep should work on the birds and fish lists provided with the starter code.

In []:
grep('birds.txt', 'er', 'birds.txt.er')

File
birds.txt.er
tern
tanager

In []:
grep('fish.txt', 'er', 'fish.txt.er')

File
fish.txt.er
mackerel
angler fish
lantern fish

In []:
grep('dir/mammals.txt', 'er', 'dir/mammals.txt.er')

File
dir/mammals.txt.er
panther