How to Use Linux Cat Command (With Examples)

Introduction

If you have worked in Linux, you surely have seen a code snippet that uses the cat command. Cat is short for concatenate. This command displays the contents of one or more files without having to open the file for editing.

In this article, learn how to use the cat command in Linux.

Prerequisites

• A system running Linux
• Access to a terminal window / command line

cat Command Syntax

To use the cat command, follow the format:

cat [options] filename(s)

[options] – This lets you issue additional instructions to the cat command. For example, to display the contents of a file with each line numbered, use the –n option:

cat –n filename

filename(s) – Specify the name of the file (or files) that you want to display. If you use more than one filename, each file will be displayed.

Linux Cat Command Examples

This article includes 15 cat commands and examples of how to use them. To try out the commands, create a couple of sample files, and test the cat commands listed below.

1. Create a New File

You can create new files and add content to them using the cat command.

Create test1.txt and test2.txt, which you can use as sample files to test out the other commands.

1. Open a terminal window and create the first file:

cat >test1.txt

2. The cursor moves to a new line where you can add the wanted text. Type a simple sentence such as:

This is test file #1.

3. To exit the prompt and write the changes to the file, hold the Ctrl key and press d.

4. Repeat the process to create test2.txt. Run:

cat >test2.txt

5. Type:

This is test file #2.

6. Press Ctrl+d.

2. Display Contents of a Single File

To display the contents of test1.txt using the cat command run:

cat test1.txt

The output displays the content as in the image below.

3. Display Contents of Multiple Files

To display the contents of both files, run the command:

cat test1.txt test2.txt

4. Redirect Contents of a Single File

Instead of displaying the contents of a file on the screen, cat can put them in a file.

cat test1.txt > test3.txt

If the destination filename doesn’t exist, it will be created. If you run cat on test3.txt, you should see the contents from test1.txt:

cat test3.txt

The output displays:

If a file is exported that already exists, this will overwrite the contents of the file:

cat test2.txt > test3.txt

cat test3.txt

The test3.txt file now has the following content:

5. Redirect Contents of Multiple Files

You can redirect the contents of multiple file into one single file:

cat test1.txt test2.txt > test3.txt

Display the content of test3.txt with:

cat test3.txt

The output shows the contents of both files, as in the image below.

6. Display the Contents in Reverse Order

The cat command can display the content of a file in reverse order (by lines). To do this, use tac (cat in reverse):

tac test3.txt

7. Append File Contents to Another File

The cat command can add the contents of a file to the end of another file. Instead of using a single > sign, use a double >> sign:

cat test1.txt >> test3.txt

Open the test3 file by running:

cat test3.txt

The content of test3 followed by test1 should display.

8. Append Text to Existing File

You can use a similar command to append text to an existing file:

cat >> test1.txt

Add a new line to the file:

This is the second line in test file #1.

Hold Ctrl and hit d.

Check the content of the test1.txt file:

cat test1.txt

9. Combine Operations

The functions of the cat command can be combined. For example, to combine the output of two files, and store the result in a new file:

cat test1.txt test2.txt > test4.txt

cat test4.txt

Alternately, you can append multiple files to the end of an existing file:

cat test2.txt test1.txt >> test4.txt

cat test4.txt

Note that the order specified is the order the files in which they are added to the destination file.

10. More and Less Options (Manage Large Files)

If you use cat on a very large file, you’ll end up with a huge string of data that’s hard to read. You can break it into pages using | more:

cat test4.txt | more

This displays a single page of the file. When you press a key, it will scroll to the next page.

If you’d like the ability to scroll forward and backward through the display, use | less.

cat test4.txt | less

11. Show Line Numbering

You may find it useful to have line numbers in the output, especially for large files. To enable line numbering, add the -n option to the cat command:

cat –n test1.txt

The output should appear as in the image below:

12. Show the End of Line

You can instruct cat to highlight the end of each line and spaces between lines with $.

To do so, use the command:

cat -e test1.txt

Since the sample file test1.txt has only one line, the output shows one $ at the end of it.

13. Show TAB Separated Lines

The cat command has the option of displaying the file content along with the tab space within the text.

To show tab separated lines for a sample run:

cat -t test4.txt

The tab space within the text is represented by ^I.

14. Remove Blank Lines

To omit blank lines from the output of cat with the –s option:

cat -t test4.txt

15. List All CAT Commands

If you have trouble remembering the options, use the --help command:

cat ––help

Conclusion

You should now have a good understanding of how to use the cat command in Linux.

Want to master more Linux commands? Check out our Linux Commands Cheat Sheet.