cat – Concatenate and Display File Contents

The cat command (short for “concatenate”) reads files sequentially, writing their contents to standard output. It is commonly used to display file contents, combine files, or create new files.

Syntax

cat [OPTION]... [FILE]...

If no files are specified, cat reads from standard input (keyboard) until EOF (Ctrl+D).

Options

Option	Description
`-n`	Number all output lines
`-b`	Number non-empty output lines only
`-s`	Squeeze multiple adjacent empty lines into one
`-E`	Display `$` at the end of each line
`-T`	Display TAB characters as `^I`
`-v`	Show non-printing characters (except tabs and line ends)

Practical Examples

1. Display the contents of a file

cat filename.txt

This prints the entire contents of filename.txt to the terminal.

2. Display contents of multiple files concatenated

cat file1.txt file2.txt

This outputs the contents of file1.txt followed immediately by file2.txt.

3. Number all lines in a file

cat -n filename.txt

Sample Output:

     1  First line of the file
     2  Second line of the file
     3  Third line of the file

4. Number only non-empty lines

cat -b filename.txt

5. Squeeze multiple empty lines into a single empty line

cat -s filename.txt

6. Show line ends explicitly with `$`

cat -E filename.txt

7. Display TAB characters as `^I`

cat -T filename.txt

8. Combine options (e.g., number non-empty lines and show line ends)

cat -bE filename.txt

9. Create a new file using `cat` and keyboard input

cat > newfile.txt

Type your content, then press Ctrl+D to save and exit.

10. Append text to an existing file

cat >> existingfile.txt

Type the additional content and press Ctrl+D when finished.

Tips

For very large files, use less or more instead of cat to view content page by page.
Combine cat with other commands using pipes.
To view hidden/control characters in files, use cat -v.

cat file.txt | grep "search_term"