I am using an opengl node to create my previews just just after a generic work item node with a couple of work items with the image output being like:

$JOB/Houdini/flip/$OS_`@pdg_index`/$OS.$F4.jpg

And it is not working the attribute doesn't expand, any tips?

Thanks.

Try using $JOB/Houdini/flip/$OS.`@pdg_index`/$OS.$F4.jpg instead - note that the $OS_ has become $OS.

The problem is that _ is a valid environment variable name token, so the expression continues to try to parse your string as an env var. That's why all of the default paths with $varaibles in ROPs/TOPs are separated with dots instead of undscores.

If that doesn't work, please attach a .hip.