Bash cat Command - Concatenate and Display Files

Using the cat Command

The cat command is used to show the content of files in the terminal.

You can also use it to combine multiple files into one.

Basic Usage

To display the content of a file, use cat filename:

cat my_file.txt
Understanding Shells
A shell is a text-based interface that lets you talk to your computer.

There are different types of shells. Bash (Bourne Again SHell)
is popular because it's powerful and easy to use.

Options

The cat command has options to change how it shows text:

• -n - Add numbers to each line
• -b - Add numbers only to lines with text
• -s - Remove extra empty lines
• -v - Show non-printing characters (except for tabs and end of line)

-n Option: Number All Lines

The -n option adds numbers to each line of the output.

cat -n my_file.txt
     1  Understanding Shells
     2  A shell is a text-based interface that lets you talk to your computer.
     3  
     4  There are different types of shells. Bash (Bourne Again SHell)
     5  is popular because it's powerful and easy to use.

-b Option: Number Non-Blank Lines

The -b option adds numbers only to lines with text, ignoring blank lines.

cat -b my_file.txt
     1  Understanding Shells
     2  A shell is a text-based interface that lets you talk to your computer.

     3  There are different types of shells. Bash (Bourne Again SHell)
     4  is popular because it's powerful and easy to use.

-s Option: Suppress Repeated Empty Lines

The -s option removes extra empty lines from the output, leaving only a single blank line where multiple ones existed.

The file notes.txt has three empty lines in a row:

cat notes.txt
First line



Second line
cat -s notes.txt
First line

Second line

-v Option: Show Non-Printing Characters

The -v option makes non-printing characters visible, except for tabs and end-of-line characters.

This is useful for debugging files with hidden characters.

Here, my_file.txt was saved with Windows line endings, so cat -v shows the hidden carriage return at the end of each line as ^M:

cat -v my_file.txt
Understanding Shells^M
A shell is a text-based interface.^M

Concatenate Two Files

The cat command can be used to concatenate multiple files into one.

This is useful for combining files or appending content to an existing file.

cat file1.txt file2.txt > combined.txt

Using cat with Piping

The cat command is often used with piping to send the content of files to other commands.

This is useful for processing text data.

cat my_file.txt | grep -i "shells"
Understanding Shells
There are different types of shells. Bash (Bourne Again SHell)