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.
- 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
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
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:
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:
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:
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:
The output displays:
If a file is exported that already exists, this will overwrite the contents of the file:
cat test2.txt > 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:
The output shows the contents of both files, as in the image below.
6. Display the Contents in Reverse Order
cat command can display the content of a file in reverse order (by lines). To do this, use
tac (cat in reverse):
7. Append File Contents to Another File
cat command can add the contents of a file to the end of another file. Instead of using a single
> sign, use a double
cat test1.txt >> test3.txt
Open the test3 file by running:
The content of test3 followed by test1 should display.
Note: If you want to remove the sample files, take a look at how to remove files and directories using the Linux command line.
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:
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
Alternately, you can append multiple files to the end of an existing file:
cat test2.txt test1.txt >> test4.txt
Note that the order specified is the order the files in which they are added to the destination file.
Note: Once you have created multiple files, you may want to group them in a single directory. Take a look at how to use mkdir command to make or create a Linux directory.
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
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
cat test4.txt | less
Note: Learn how to use the Linux split command to easily manage text files with many lines.
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 –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
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
cat -t test4.txt
15. List All CAT Commands
If you have trouble remembering the options, use the
Note: Learn how to concatenate strings in Bash.
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 list of Linux Commands All Users Should Know.