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

A simpler option in my opinion is :

echo -e 'task goes here\n$(cat todo.txt)' > todo.txt

This works because the command inside of $(...) is executed before the file is overwritten with > todo.txt

While the other answers work fine, I find this much easier to remember because I use echo and cat every day.

Answer 3

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 4

If the text file is small enough to fit in memory, you don't have to create a temporary file to replace it with. You can load it all into memory and write it back out to the file.

echo "$(echo 'task goes here' | cat - todo.txt)" > todo.txt

It's impossible to add lines to the beginning of the file without over writing the whole file.

Answer 5

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

Answer 6

The moreutils have a nice tool called sponge:

echo "task goes here" | cat - todo.txt | sponge todo.txt

It'll "soak up" STDIN and then write to the file, which means you don't have to worry about temporary files and moving them around.