I have no HP-UX experience but where I’ve needed to create properties that cater for Windows / Linux / Mac OS and I try to use a standard approach to cater for supporting a mixture of OS’s within a single fixlet/property.
Firstly I would list out what paths you have for each OS then build a relevance statement that covers the pathname for each OS. For Windows, Linux / Mac I use this as a guideline
((if (windows of it) then (folder "WidowsPathHere") else (if(unix of it) then (If(name of it as lowercase contains "linux") then (folder "LinuxPathHere") else (folder "UnixPathHere")) else (if(mac of it) then ("MacPathHere") else (nothing)))) of operating system)
Then, build relevance to parse the file based on its format (assuming the format is common across the various OS). An example of parsing a common formed text file across OS like this can be seen in Universal append to hosts file which may help you construct something for your specific use case.