How do you insert a text before the first line in your file?

I've been looking around sed command to add text into a file in a specific line. This works adding text after line 1:

sed '1 a\

But I want to add it before line 1. That would be so

sed '0 a\

but I get this error: invalid usage of line address 0 .

What's your suggestion?

Use sed 's insert ( i ) option which will insert the text in the preceding line.

sed '1 i\

Question author's update:

To make it edit the file in place - with GNU sed - I had to add the -i option:

sed -i '1 i\anything' file

Also syntax

sed  -i '1i text' filename

For non-GNU sed

You need to hit the return key immediately after the backslash 1i\ and after first_line_text .

sed -i '1i\
first_line_text
'

Also note that some non-GNU sed implementations (for example the one on macOS) require an argument for the -i flag (use -i '' to get the same effect as with GNU sed ).

For sed implementations that does not support -i at all, run without this option but redirect the output to a new file. Then replace the old file with the newly created file