Linux / Unix: Use Cat Command To Append Data To a File

Redirection symbol

• >> filename : Appends standard output to file.

Syntax

The syntax is:

cat file >> file2
echo 'text to append' >> file2
printf "text to append\n" >> fileName

Examples

Create a text file called foo.txt, type:

cat > foo.txt
This is a test.
I like Unix operating systems.

To save the changes press CTRL-d i.e. press and hold CTRL and press d. Create another text file called bar.txt as follows:

echo 'For desktop usage I prefer Apple OS X unix operating systems.' > bar.txt

Display both files on sceen, enter:

cat foo.txt
cat bar.txt

To append a contains of bar.txt to to foo.txt, enter:

cat bar.txt >> foo.txt
cat foo.txt

To append a ‘Use unix or die’ text to foo.txt file, enter:

echo 'Use unix or die' >> foo.txt
cat foo.txt

Sample outputs:

Fig.01: Using the cat and echo command to append a text to a file.

Append text to a file when using sudo command

We can use the echo command or printf command to append data to a file called sales.txt in the current directory:

echo 'some data' | sudo tee -a sales.txt
echo '1192.168.1.253 wireless-router' | sudo tee -a /etc/hosts

Want to append to a file? Try:
cat filename | sudo tee -a foo_file.txt
In this example append data using the following syntax:
sudo sh -c 'echo "192.168.1.253 wireless-router" >> /etc/hosts'
Verify it:
cat /etc/hosts