I have this channel expression: which sets the name of a saved output. Now let's say `chs("../../null1/shot")` is 1 and $OS is "file". In this form, it works as expected and Houdini resolves the name as file1.exr
If I edit the path to:
Houdini resolves the name as 1.exr instead of file_1.exr.
Is there a way to incorporate an underscore in a filename referencing the value of another parameter?

Cheers,
Ivan

Yep, that appears to be a bug.
What does work is the dash character. Try that instead.

be sure to enclose variables with `` as well to avoid this kind of problems.
In your case Houdini try to resolve the non existing variable "$OS_" ....

Andr
In your case Houdini try to resolve the non existing variable "$OS_"

And to avoid this ambiguity you can use {} to hint where your variable name is ending

So in your case ${OS}

Thanks guys! ${OS} solved the issue.

Cheers,
Ivan