How do I insert a line at the top of a text file using the command line?

Question

I want to insert text at the top of an already existing file. How can I achieve this. I tried echo and tee but was not successful.

I was trying to insert repo line at the top of sources.list file from terminal.

Note

I need an one line quick solution, because another answer's method was known to me already

Answer 1

It's actually quite easy with sed:

• sed -i -e '1iHere is my new top line\' filename

• 1i tells sed to insert the text that follows at line 1 of the file; don't forget the \ newline at the end so that the existing line 1 is moved to line 2.

Answer 2

In general editing in place with a script is tricky, but you can use echo and cat and then mv

echo "fred" > fred.txt
cat fred.txt t.txt >new.t.txt
# now the file new.t.txt has a new line "fred" at the top of it
cat new.t.txt
# can now do the rename/move
mv new.t.txt t.txt

However if you're playing with sources.list you need to add in some validation and bullet-proofing to detect errors etc because you really don't want to loose this. But that's a separate question :-)

Answer 3

There is always the awk option. Replace string variable with your contents. This is not an in-place change though. Personally, I tend to not make in-place changes. This is definitely a personal preference. Two things, -v signifies a variable in awk and variable n is used here to match a line number, effectively NR == 1. You could use this in any number of ways just by changing the value of n and s.

string="My New first line"; awk -v n=1 -v s="$string" 'NR == n {print s} {print}'     file.source > file.target

Example:

% cat file.source                                                                                                                                      

First Line
Second Line
Third Line

% string="Updated First Line"; awk -v n=1 -v s="$string" 'NR == n {print s} {print}' file.source > file.target; cat ./file.target                      !698

Updated First Line
First Line
Second Line
Third Line