bash Add incremental number before string

Question

how can I add an incremental number in from of a list of strings?

example:

cat names.txt

alpha
beta
gamma

I need a loop, which inserts a number before the string.. like this

1. alpha
2. beta
3. gamma

could that be possible in bash?

Answer 1

The command line util nl (= number lines) is made exactly for this:

nl -w 1 -s '. ' names.txt

prints

1. alpha
2. beta
3. gamma