Tee

You can use tee instead of double redirection modifier >> as the implementation of the redirection modifier >> on different linux distributions is inconsistent.

You can append to a file by using the tee command with the echo of what you want to append piped | to the command. The -a flag indicates that the text you should appended to the target file.

$ echo "some text" | tee -a file.txt

If you have problems with user permissions you can sudo the tee part of the command.

$ echo "some text" | sudo tee -a file.txt