Shell Programming and Scripting

please help:
I want to append the word "world" after every line that ends with hello:
$cat file
hello
hello$ sed '/hello/ a world' file
sed: Function /hello/ a world cannot be parsed.

What's wrong with the above command??

If a hit a new line it works:
$ sed '/hello/ a\
> world' file
hello
world
hello
world

How to make the first call work (without new line)???

Andy

Andy,
To append "string2" to the end of every line that ends with "string1":

Code:

sed 's/string1$/&string2/' input_file