Learn to use ‘CAT’ command in linux
The cat (short for “concatenate“) command is one of the most frequently used command in Linux/Unix like operating systems. cat command allows us to create single or multiple files, view contain of file, concatenate files and redirect output in terminal or files.
Cat stands for “concatenate.” It reads data from files, and outputs their contents. It is the simplest way to display the contents of a file at the command line.
cat is one of the most commonly-used commands in Linux. It can be used to:
- Display text files.
- Copy text files into a new document.
- Append the contents of a text file to the end of another text file, combining them.
The basic syntax is as follows:
- cat filename
- cat > filename
- cat [options] filename
- cat file1
- cat > file2
- cat file3 | command
- cat file4 | grep something
Cat command examples
1. Display Contents of File
In the below example, it will show contents of /etc/passwd file.
2. View Contents of Multiple Files in terminal
In below example, it will display contents of test & test1 file in terminal.
3. Create a File with Cat Command
We will create a file called test2 file with below command.
Awaits input from user, type desired text and press CTRL+D (hold down Ctrl Key and type ‘d‘) to exit. The text will be written in test2 file. You can see content of file with following cat command.
4. Use Cat Command with More & Less Options
If file having large number of content that won’t fit in output terminal and screen scrolls up very fast, we can use parameters more and less with cat command as show above.
5. Display Line Numbers in File
With -n option you could see the line numbers of a file song.txt in the output terminal.
6. Display $ at the End of File
In the below, you can see with -e option that ‘$‘ is shows at the end of line and also in space showing ‘$‘ if there is any gap between paragraphs. This options is useful to squeeze multiple lines in a single line.
7. Display Tab separated Lines in File
In the below output, we could see TAB space is filled up with ‘^I‘ character.
8. Display Multiple Files at Once
In the below example we have three files test, test1 and test2 and able to view the contents of those file as shown above. We need to separate each file with ; (semi colon).
9. Use Standard Output with Redirection Operator
We can redirect standard output of a file into a new file else existing file with ‘>‘ (greater than) symbol. Careful, existing contents of test1 will be overwritten by contents of test file.
10. Appending Standard Output with Redirection Operator
Appends in existing file with ‘>>‘ (double greater than) symbol. Here, contents of test file will be appended at the end of test1 file.
11. Redirecting Standard Input with Redirection Operator
When you use the redirect with standard input ‘<‘ (less than symbol), it use file name test2 as a input for a command and output will be shown in a terminal.
12. Redirecting Multiple Files Contain in a Single File
This will create a file called and all output will be redirected in a newly created file.
13. Sorting Contents of Multiple Files in a Single File
This will create a file test4 and output of cat command is piped to sort and result will be redirected in a newly created file.
This article shows the basic commands that may help you to explore cat command. You may refer man page of cat command if you want to know more options.