[SunHELP] insert one line at beginning of text file; efficiently

[sunhelp at sunhelp.org]

I need to insert a line at the beginning of text files and would like to
know if the following would be the most efficient way of doing so.

$ cat test.txt
This is the original test data. 
$ echo "new line" > tmp.new
$ cat test.txt >> tmp.new
$ mv tmp.new test.txt
$ cat test.txt
new line
This is the original test data.

This code will be intercepting print data which could be lengthy and 
that is why I am concerned with efficiency.  If I have to go with temp
files I will add a time stamp to avoid multiple tasks overwritting 
each other.

TIA

Solaris 8