How can I add a line to a file in a shell script?

Question

I want to add a row of headers to an existing CSV file, editing in place. How can I do this?

echo 'one, two, three' > testfile.csv

and I want to end up with

column1, column2, column3
one,     two,     three

Changing the initial CSV output is out of my hands.

Any standard command will do. The important thing is the file is edited in place, and the line is inserted at the beginning of the file.

Answer 1

To answer your original question, here's how you do it with sed:

sed -i '1icolumn1, column2, column3' testfile.csv 

The "1i" command tells sed to go to line 1 and insert the text there.

The -i option causes the file to be edited "in place" and can also take an optional argument to create a backup file, for example

sed -i~ '1icolumn1, column2, column3' testfile.csv 

would keep the original file in "testfile.csv~".

Answer 2

This adds custom text at the beginning of your file:

echo 'your_custom_escaped_content' > temp_file.csv cat testfile.csv >> temp_file.csv mv temp_file.csv testfile.csv 

Answer 3

This doesn't use sed, but using >> will append to a file. For example:

echo 'one, two, three' >> testfile.csv

Edit: To prepend to a file, try something like this:

echo "text"|cat - yourfile > /tmp/out && mv /tmp/out yourfile

I found this through a quick Google search.