How do I add text to the beginning of a file in Bash?

Question

Hi I want to prepend text to a file. For example I want to add tasks to the beginning of a todo.txt file. I am aware of echo 'task goes here' >> todo.txt but that adds the line to the end of the file (not what I want).

Answer 1

echo 'task goes here' | cat - todo.txt > temp && mv temp todo.txt

or

sed -i '1s/^/task goes here\n/' todo.txt

or

sed -i '1itask goes here' todo.txt

Answer 2

You can create a new, temporary file.

echo "new task" > new_todo.txt
cat todo.txt >> new_todo.txt
rm todo.txt
mv new_todo.txt todo.txt

You might also use sed or awk. But basically the same thing happens.

Answer 3

You cannot insert content at the beginning of a file. The only thing you can do is either replace existing content or append bytes after the current end of file.

Any solution to your question then requires a temporary file to be created (on memory or on disk) which will eventually overwrite the original file.

Beware not loosing data by preserving the original file while building the new one, should the file system happen to be full during the process. eg:

cat <(echo task go there) todo.txt > todo.txt.new && mv todo.txt.new todo.txt