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Linux Cat Command

The cat command is one of the most widely used command in Linux. The name of the cat
command comes from its functionality to concatenate files. It can read and concatenate files, writing their contents to the standard output. If no file is specified or if the input file name is specified as a single hyphen (-
) it reads from the standard input.
Cat is most commonly used to display the contents of one or multiple text files, combine files by appending the contents of one file to the end of another file, and create new files.
In this tutorial, we will show you how to use the cat command through practical examples.
Cat Command Syntax
Before going into how to use the cat command, let’s start by reviewing the basic syntax.
The cat utility expressions take the following form:
cat [OPTIONS] [FILE_NAMES]
OPTIONS
- cat options. Usecat --help
to view all available options.FILE_NAMES
- Zero or more file names.
Displaying File Contents with Cat
The most basic and common usage of the cat command is to read the contents of files.
For example, the following command will display the contents of the /etc/issue
file in the terminal:
cat /etc/issue

Redirect Contents of File
Instead of displaying the output to stdout (on the screen) you can redirect it to a file.
The following command will copy the contents of file1.txt
to file2.txt
using the (>
) operator :
cat file1.txt > file2.txt
Normally you would use the cp
command to copy a file.
If the file2.txt
file doesn’t exist the command will create it. Otherwise it will overwrite the file.
Use the (>>
) operator to append the contents of file1.txt
to file2.txt
:
cat file1.txt >> file2.txt
Same as before, if the file is not present it will be created.
Print Line Numbers
To display contents of a file with line numbers use the -n
argument:
cat -n /etc/lsb-release
1 DISTRIB_ID=Ubuntu
2 DISTRIB_RELEASE=18.04
3 DISTRIB_CODENAME=bionic
4 DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"
Suppress Repeated Empty Lines
Use the -s
argument to omit the repeated empty output lines:
cat -s file.txt
Display TAB characters
Use the -T
argument to visually distinguish between tabs and spaces.
cat -T /etc/hosts
127.0.0.1^Ilocalhost
127.0.1.1^Iubuntu1804.localdomain
The TAB characters will be displayed as ^I
.
Display End of Lines
To display the invisible line ending character use the -e
argument:
cat -e /etc/lsb-release
DISTRIB_ID=Ubuntu$
DISTRIB_RELEASE=18.04$
DISTRIB_CODENAME=bionic$
DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"$
The Line endings will be displayed as $
.
Concatenating Files with Cat
When passing two or more file names as arguments to the cat command the files contents will be concatenated. Cat reads the files in the sequence given in its arguments and displays the files contents in the same sequence.
For example, the following command will read the contents of file1.txt
and file2.txt
and display the result in the terminal:
cat file1.txt file2.txt
You can concatenate two or more text files and write them to a file.
The following command will concatenate the contents of file1.txt
and file2.txt
and write them to a new file combinedfile.txt
using the (>
) operator :
cat file1.txt file2.txt > combinedfile.txt
If the combinedfile.txt
file doesn’t exist the command will create it. Otherwise it will overwrite the file.
To concatenate the contents of file1.txt
and file2.txt
and append the result to file3.txt
to use the (>>
) operator:
cat file1.txt file2.txt >> file3.txt
If the file is not present it will be created.
When concatenating files with cat, you can use the same arguments as shown in the previous section.
Creating Files with Cat
When creating a small file it is much easier to use cat instead of using Vim, Sublime Text, Visual Studio Code or any other text editor.
To create a new file use the cat command followed by the redirection operator (‘>’) and the name of the file you want to create. Press Enter
type the text and once you are done press the CRTL+D
to save the files.
In the following example we are creating a new file named file1.txt
:
cat > file1.txt

In the following example we are creating a new file named file1.txt
:
cat > file1.txt
If a file named file1.txt
is present it will be overwritten. Use the (‘>>’) operator to append the output to an existing file.
Conclusion
By now you should have a good understanding of how to use the Linux cat command.
If you have any question or feedback feel free to leave a comment.