Paste

Combine file contents joining rows with delimiters

#file1.txt
a345
b2
c457
d3

#file2.txt
1
2
3
4

$ paste file1.txt file2.txt
a345  1
b2    2
c457  3
d3    4

$ paste -d ':' file1.txt file2.txt
a345:1
b2:2
c457:3
d3:4

Join

Same as join checking common columns

$ cat phonebook
555-123-4567 Bob
555-231-3325 Carol
555-340-5678 Ted
555-289-6193 Alice    

$ cat directory
555-123-4567 Anytown
555-231-3325 Mytown
555-340-5678 Yourtown
555-289-6193 Youngstown    

The result of joining these two file is as shown in the output of the following command:

$ join phonebook directory
555-123-4567 Bob Anytown
555-231-3325 Carol Mytown
555-340-5678 Ted Yourtown
555-289-6193 Alice Youngstown