Posted on September 15, 2023 by nexonhost
How To Use Join Command.
Linux is an open-source operating system that provides users with a wide range of utilities and tools for managing and manipulating data. One such tool is join command, which is used to join two different files based on a common field. join command is a very useful utility that can be used to merge or join two files, where one file contains a list of unique fields and other file contains more detailed information about those fields.
The Linux join command is a powerful tool that is used to merge two different files based on a common field. command reads contents of two files and merges them based on specified field, which can be a string or a numeric value. In this article, we will discuss various aspects of join command and its usage.
Syntax
The syntax for join command is as follows −
join [options] file1 file2
The options for join command are as follows −
-t − This option is used to specify delimiter character used in files. By default, delimiter is a blank space.
-1 − This option is used to specify field number in first file.
-2 − This option is used to specify field number in second file.
-a − This option is used to print all lines from both files, including those that do not match.
-e − This option is used to replace missing fields with a specified value.
Examples
Let’s now take a look at some examples of join command.
Example 1
Suppose we have two files, file1 and file2, with following contents −
File 1 −
1 Alpha 2 Bravo 3 Charlie 4 Delta 5 Echo
File 2 −
2 20 3 30 4 40 5 50 6 60
We can join these two files based on first field in each file using following command −
join file1 file2
The output will be as follows −
2 Bravo 20 3 Charlie 30 4 Delta 40 5 Echo 50
As we can see, join command has merged two files based on first field.
Example 2
Now suppose we have two files, file1 and file2, with following contents −
File 1 −
A Alpha B Bravo C Charlie D Delta E Echo
File 2 −
B 20 C 30 D 40 E 50 F 60
We can join these two files based on second field in each file using following command −
join -1 2 -2 1 file1 file2
The output will be as follows −
Bravo B 20 Charlie C 30 Delta D 40 Echo E 50
As we can see, join command has merged two files based on second field.
Example 3
Suppose we have two files, file1 and file2, with following contents −
File 1 −
1 Alpha 2 Bravo 3 Charlie 4 Delta 5 Echo
File 2 −
2 20 3 30 4 40 5 50 6 60
We can join these two files and include all lines from both files, including those that do not match, using following command −
join -a 1 -a 2 file1 file2
The output will be as follows −
1 Alpha 2 Bravo 20 3 Charlie 30 4 Delta 40 5 Echo 50 6 60
As we can see, join command has merged two files and included all lines from both files.
Here are some additional points to consider when working with Linux join command −
The join command requires that input files be sorted based on join field. If files are not sorted, join operation will not work correctly. You can use sort command to sort files before using join command.
If join field contains spaces or other special characters, you may need to specify a delimiter character using -t option. For example, if join field is separated by commas, you can use -t ‘,’ to specify delimiter.
The join command only works with two input files. If you need to join more than two files, you can use output of one join operation as input for another join operation.
The join command can be used with various output options to control format of output. For example, you can use -o option to specify output format, such as join field followed by remaining fields in file 1 and file 2.
If you want to exclude matching lines from output, you can use -v option. This will only print lines from file 1 or file 2 that do not have a match in other file.
If join field contains duplicate values in either file, join command will create a cross-product of matching lines. To avoid this, you can use uniq command to remove duplicate lines before using join command.
Overall, Linux join command is a versatile tool that can be used for various data processing tasks. By mastering usage and options of join command, you can greatly improve your efficiency and productivity when working with large datasets in Linux.
Conclusion
In conclusion, Linux join command is a very useful utility that can be used to merge two different files based on a common field. command provides various options to customize join operation, such as specifying delimiter character, field numbers, and output format. join command is particularly useful in situations where we need to combine data from multiple files and create a single output file for further processing.