Cat and Tac Command Usage in Linux

The cat command is pretty useful for reading, creating, and concatenating files. While the tac command also works similarly to the cat command, which outputs the last line first.

Tutorial Details

Description	Cat and Tac command
Difficulty Level	Low
Root or Sudo Privileges	Maybe
Host System and Architecture	Ubuntu 22.10 (x64)
OS Compatibility	Ubuntu, Manjaro, Fedora, etc.
Prerequisites	cat, tac
Internet Required	No
Discussed Tools in this Article

Also Read: Grep Command in Linux

Reading a File

Define the path of the text file, and the cat command will output the content.

$ cat /path/to/file.txt

Creating a File

Create a blank new file using the cat command with the redirection symbol.

$ cat > file.txt

If “file.txt” exists in the present directory, the above command will remove its content.

Creating a File Without Removing Old Content

The following command will create a new file if it’s not exists or hold the content if file already present in the directory without removing any content.

$ cat >> file.txt

Reading Multiple Files

You can specify as many files as you want to read using the cat command, separating each with a space.

$ cat file1.txt file2.txt

Reading All Files in the Directory Sharing Similar Extensions

If you have a directory with a bunch of files with the “.txt” extension, you can easily read all of the files’ content using the following command:

$ cat *.txt

Redirect Output to a New File

If you want to save the output of two or more files into a new file, use the following command.

$ cat file1.txt file2.txt >> newfile.txt

If “newfile.txt” is already present in the current directory, then new content will be appended.

Redirect Output of All Files in Directory to New File

If you are present in a directory with a bunch of “.txt” files and want to output all files to a new file, use the following command.

$ cat *.txt >> newfile.txt

If “newfile.txt” already exists in the present directory, then new content will be appended.

Remove Multiple Spaces

Configuration or programming files contain multiple repeated blank lines that make them larger and more difficult to read, which can be easily replaced with one blank line using the following command.

$ cat -s file.txt

Using More and Less Options

If your file is too large to read, use the more or less options to display the single screen content of the file by going down one page at a time using the down arrow key.

$ cat file.txt | more
$ cat file.txt | less

Print the Line Number in the File

You can easily get the line number in front of each line, making it easier to find lines in a file, using the following command.

$ cat -n file.txt 
     1 HELLO
     2 Linux
     3 TLDR
     4 READER

Print $ at the End of the Line

Large lines in file make it difficult to find the end of the line, which can be easily spotted by placing “$” at the end of each line using the -e flag.

$ cat -e file.txt 
     HELLO$
     Linux$
     TLDR$
     READER$
     This is new line in the file$

Sorting File Content

If you have numbers in a file arranged in random order, you can easily sort them from ascending to descending using the following command.

$ cat file.txt | sort
1
2
3
4
5
6

Print the File Content in Reverse Order

If you have a sorted number or want to read the last line first, use the tac command instead of the cat command as shown.

$ tac file.txt 
line number six
line number five
line number four
line number three
line number two
line number one

That’s all for now. If you have any more examples, do let us know in the comment section.