How Do You Concatenate Files in UNIX Shell Scripting?


Heather Bennett

How Do You Concatenate Files in UNIX Shell Scripting?

Concatenating files is a common operation in UNIX shell scripting that allows you to combine the contents of multiple files into a single file. This can be useful when you want to merge log files, concatenate text files, or combine the output of different commands. In this tutorial, we will explore various methods to concatenate files using shell scripting.

Method 1: Using the cat Command

The most straightforward way to concatenate files in UNIX is by using the cat command. The syntax for concatenating two or more files is as follows:

$ cat file1.txt file2.txt > output.txt

This command will concatenate the contents of file1.txt and file2.txt, and then redirect the output to output.txt. If output.txt already exists, it will be overwritten. If you want to append the contents instead of overwriting, use double greater-than sign (>>).

Method 2: Using the paste Command

If you want to concatenate files side by side rather than line by line, you can use the paste command. This is particularly useful when merging columns from different files. The basic syntax for using paste is:

$ paste file1.txt

The above command will merge the lines from file1.txt, separated by a tab character (by default), and save the result to output.

Merging Columns with Paste

If you want to merge the files column-wise, you can use the -d option followed by a delimiter. For example:

$ paste -d ',' file1.txt

This command will merge the lines from file1.txt, separated by a comma, and save the result to output.

Method 3: Using Input Redirection (<

An alternative way to concatenate files is by using input redirection with the <

$ cat <<EOF > output.txt

In this example, we are redirecting the contents of file1.txt into output. The <

Merging Files with a Separator using Input Redirection (<

If you want to add a separator between each file’s content while concatenating, you can modify the above command as follows:

$ cat <<EOF > output.txt
$(cat file1.txt)
$(cat file2.txt)

In this modified example, we are appending “—” as a separator between the contents of file1.

Note: Remember to use appropriate file paths or names based on your system configuration.


In this tutorial, we have explored different methods to concatenate files in UNIX shell scripting. The cat command is the simplest and most commonly used method, while the paste command provides more flexibility for merging columns.

Additionally, we have learned how to use input redirection with <