You can combine multiple files together using the paste command.
If you have a file named numbers.txt (that’s literally just a list of
numbers) and a file you’d like numbered (say greatcities.txt), then you can
use the below to give you the list printed to the terminal.
$ paste numbers.txt greatcities.txt
1 Heidelberg
2 Chicago
3 New Lenox
4 Denton
5 Kirksville
Obviously, you can use > to direct the
output to a new file.
It is also good to note that default paste use will create the output with a
tab delimiter.
Changing delimiters can be done through the -d flag.