dear all,
i am fresh for unix, and currently i wish to insert a line into a txt file as below:

test.txt
------
abc
def
ghi

and i wish to insert "hello world" in between abc and def line:

output wanted:
------------------
abc
hello world
def
ghi

what should be the "sed" use?

Here's an awkward awk bit:

$ cat testfile
abc
def
ghi
$ awk 'NR==2 {printf "hello world\n"} {print $0}' testfile
abc
hello world
def
ghi

thanks alot ..it 's working!!

If you want to use sed

# sed '/abc/ a\
hello world!' test.txt

How do you make the changes permanent in the file. I want to be able to save the changes from the awk command.

i tried the example above, then issued the cat command but the "hello world" wasnt saved to the file.

$ cat testfile
abc
def
ghi


Also when I try the command with a file called file11 with the following data:
Line1
Line2
Line3

I get the following output:
Line1hello world
Line2Line3

awk 'NR==2 {printf "hello world\n"} {print $0}' testfile > newfile

Great thanks. That solved the problem of how to save it.
The other problem that I have is that the output seems to join together whereas I want it inserted in a new line.

e.g. file1 with the following data
Line1
Line2
Line3


When I check the results in the file it saves to, the output comes out like this:

Line1Hello world
Line2Line3


Whereas I would like the output to be as follows:

Line1
Hello world
Line2
Line3