What Is Cat Command

Terminal window showing the output of a cat command

The cat command in Linux displays file contents, concatenates files, and creates new ones. It's a basic but essential utility for working with text files in the terminal.

How the Cat Command Works

The cat command reads files sequentially and writes their contents to standard output (usually the terminal). It can handle multiple files at once, combining them into a single output stream. The name "cat" is short for "concatenate," reflecting its primary function.

For example, running cat file.txt prints the contents of file.txt to the terminal. To view multiple files, use cat file1.txt file2.txt, which displays both files in sequence.

Main Functions of the Cat Command

The cat command supports several options, including:

-n: Number all output lines.
-b: Number non-blank output lines.
-s: Squeeze multiple adjacent empty lines into one.

A common use case is creating a new file. For example, cat > newfile.txt allows you to type text directly into newfile.txt until you press Ctrl+D to save and exit.

Common Misconceptions About Cat Command

Some users confuse cat with other commands like less or more, which are used for viewing large files page by page. Unlike those, cat outputs the entire file at once, which can be overwhelming for large files.

Another mistake is using cat to search within files. While you can pipe its output to grep (e.g., cat file.txt | grep "search term"), it's often more efficient to use grep directly on the file.

Example: Using Cat Command to View and Concatenate Files

Suppose you have two files, file1.txt and file2.txt, and you want to combine them into a single file called combined.txt. You can do this with the following command:

cat file1.txt file2.txt > combined.txt

This reads both files and writes their contents into combined.txt.

To view the contents of combined.txt, simply run:

cat combined.txt

This prints the combined contents of both original files to the terminal.

When to Use Cat Command

The cat command is useful for quick tasks like checking small files, combining files, or creating new ones. However, for large files, consider using less or more to avoid overwhelming your terminal with too much output at once.

Conclusion

The cat command is a versatile tool for displaying and manipulating text files in Linux. creating new ones, cat provides a simple and efficient solution.