Master the Linux cat Command: From Simple Viewing to Advanced Redirection

In Linux, cat is not a cat but a command that prints the contents of text files to the terminal.

Using the cat command

The basic syntax is: cat [options] Filename(s) [options] modify cat’s default behavior, e.g., -n to number lines. Filename is the name of the file to read.

1. Create a new file

You can create a file with cat > Filename. After running the command, a blinking cursor appears; type the desired content and press Ctrl+D to save. Pressing Ctrl+D immediately creates an empty file.

cat > NewFile.txt

2. Copy file contents to another file

Redirect the output of one file to another: cat FileA > FileB This overwrites FileB with the contents of FileA. You can also copy multiple files at once:

cat FileA FileB > FileC

3. Append a file’s content to another file

Use the double‑greater‑than operator >> to add data without overwriting:

cat FileA >> FileB

4. Show line numbers

Display a file with line numbers using the -n option:

cat -n File

5. Delete empty lines

Pipe cat’s output to grep -v '^$' to filter out blank lines: cat File | grep -v '^$' You can redirect the filtered result to a new file:

cat File | grep -v '^$' > NewFile

Summary of common cat usages

cat <Filename>

– Print file contents to the terminal. cat > File – Create a new file (or overwrite) and write content. cat FileA > FileB – Replace FileB with FileA 's contents. cat FileA >> FileB – Append FileA to FileB. cat -n File – Show line numbers. cat File | more – Page through a large file. cat File | less – Page with bidirectional scrolling. cat File | grep -v '^$' – Remove all empty lines.

Practice using different options and files to reinforce what you’ve learned.