Using Sed to expand environment variables inside files

Question

I\'d like to use Sed to expand variables inside a file.

Suppose I exported a variable VARIABLE=something, and have a \"test\" file with the following:

Answer 1

Maybe you can get by without using sed:

$ echo $VARIABLE
something
$ cat test
I'd like to expand this: ${VARIABLE}
$ eval "echo \"`cat test`\"" > outputfile
$ cat outputfile
I'd like to expand this: something

Let shell variable interpolation do the work.