Introduction

Join command is yet another example of text processing utility under GNU/Linux. Join command combines two files based on the matching content lines found in each file. Using join command is quite straight forward and if used currently and in the right situation it can save lots of time and effort. This article requires very basic command line experience.

Frequently used options

• -1 FIELD
  Join on specified field found in file 1
• -2 FIELD
  Join on specified field found in file 2
• -t CHAR
  Use CHAR as an input and output separator

Basics

Basic usage of join command is usage without any options. All what is required is to specify 2 files as an arguments. Let’s say we have two files A.txt and B.txt with a following content:

$ cat A.txt
1 A
2 B
3 C
$ cat B.txt
1 John
2 Linda
3 Rares

Here we can see that first field is a perfect candidate to perform a join operation upon. By default join command will perform join operation on a first FIELD where field separator is single space character or TAB. Therefore, by executing a following command our two files are joined based on FIELD 1:

$ join A.txt B.txt
1 A John
2 B Linda
3 C Rares