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replace only the first line of a file without temporary files

hello I have a file in which I want to replace the first line with the context of another file. I have done this with temporary files, with I want to know if there is an easier and more efficient way to do this with sed, awk or other stream editor.

I have a main file whose content is:
header

text...
...
text...

I have a file that has the text I want to insert in the fist line.
The output I want is

newHeader

text...
...
text...

How can I do this without using temporary files? Thanks

Hi,

As always there are probably others ways of doing this, but this should work:

- A sed solution -

Code:

#!/bin/bash

sed -i '/header/ {

  r newheader

  d

}' $1

Sed searches for header (the /header/ part) and if found replace it with the content of the file called newheader (the r newheader and d part). The -i saves changes immediately.

Files used and testrun:

Quote:

cat mainfile

a one line header

Text text .......
Text text .......

Text text .......

Text text .......

cat newheader
This is

--- The New Header ---

that's all folks

./replaceheader mainfile

This is

--- The New Header ---

that's all folks

Text text .......
Text text .......

Text text .......

Text text .......