If I have output from two sources that I want to put together on the same line, how would I do that?

In my case I have a file and a program. The file is something like this:

```
listOfThings=

```

My program outputs a list of strings on a single line. I want have a small script that runs nightly to put these two things together on a single line. I can't figure out how to do this right though

example batch file

```
type header.txt > outputfile.txt
myProgram >> outputfile.txt

```

which results in this:

```
listOfThings=
foo bar baz etc

```

I really need the output file to have the list immediately follow the =, but I can't figure out how to do it with the >> operator. (and before anyone suggests it, I can't do something like put a \ on the end of the listOfThings= line, that won't work for what I'm trying to do)