Cat Command in Linux
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The cat command is one of the most widely used commands 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. Use
cat --helpto view all available options.
FILE_NAMES- Zero or more file names.
Displaying File Contents
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:
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
file2.txt using the (
>) operator :
cat file1.txt > file2.txt
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
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
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
-s option to omit the repeated empty output lines:
cat -s file.txt
Display TAB characters
-T option allows you to visually distinguish between tabs and spaces.
cat -T /etc/hosts
The TAB characters will be displayed as
Display End of Lines
To display the invisible line ending character use the
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
When passing two or more file names as arguments to the
cat command the contents of the files will be concatenated.
cat reads the files in the sequence given in its arguments and displays the file's contents in the same sequence.
For example, the following command will read the contents of
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
file2.txt and write them to a new file
combinedfile.txt using the (
>) operator :
cat file1.txt file2.txt > combinedfile.txt
combinedfile.txt file doesn't exist, the command will create it. Otherwise, it will overwrite the file.
To concatenate the contents of
file2.txt and append the result to
file3.txt to use the (
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.
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 file.
In the following example, we are creating a new file named
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.
cat >> file1.txt
cat command can display, combine and create new file.
If you have any questions or feedback, feel free to leave a comment.