How do I append text to a file?

Question

How about:

echo "hello" >> <filename>

Using the >> operator will append data at the end of the file, while using the > will overwrite the contents of the file if already existing.

You could also use printf in the same way:

printf "hello" >> <filename>

Note that it can be dangerous to use the above. For instance if you already have a file and you need to append data to the end of the file and you forget to add the last > all data in the file will be destroyed. You can change this behavior by setting the noclobber variable in your .bashrc:

set -o noclobber

Now when you try to do echo "hello" > file.txt you will get a warning saying cannot overwrite existing file.

To force writing to the file you must now use the special syntax:

echo "hello" >| <filename>

You should also know that by default echo adds a trailing new-line character which can be suppressed by using the -n flag:

echo -n "hello" >> <filename>

References

• echo(1) - Linux man page
• noclobber variable
• I/O Redirection

cat >> filename
This is text, perhaps pasted in from some other source.
Or else entered at the keyboard, doesn't matter. 
^D

Essentially, you can dump any text you want into the file. CTRL-D sends an end-of-file signal, which terminates input and returns you to the shell.

Other possible way is:

echo "text" | tee -a filename >/dev/null

The -a will append at the end of the file.

If needing sudo, use:

echo "text" | sudo tee -a filename >/dev/null

Follow up to accepted answer.

You need something other than CTRL-D to designate the end if using this in a script. Try this instead:

cat << EOF >> filename
This is text entered via the keyboard or via a script.
EOF

This will append text to the stated file (not including "EOF").

It utilizes a here document (or heredoc).

However if you need sudo to append to the stated file, you will run into trouble utilizing a heredoc due to I/O redirection if you're typing directly on the command line.

This variation will work when you are typing directly on the command line:

sudo sh -c 'cat << EOF >> filename
This is text entered via the keyboard.
EOF'

Or you can use tee instead to avoid the command line sudo issue seen when using the heredoc with cat:

tee -a filename << EOF
This is text entered via the keyboard or via a script.
EOF