A script to download the components for a macOS installer from Apple's softwareupdate servers and then install those components as a working "Install macOS High Sierra.app" onto a disk image.
The install logic within Apple's packages will be evaluated by Apple's installer, so you must run this on hardware compatible with the version of macOS for which you are attempting to obtain an installer. In other words, this script will fail when run on hardware that does not support High Sierra, and should High Sierra be "forked" as it was when the iMac Pro was first shipped, you may only be able to successfully install a hardware-specific version of the installer on the hardware supported by that specific build.
You'll need roughly twice the ultimate storage space; IOW if the High Sierra installer is 6GB you'll need at least 12GB free. If you use the --compress option you may need up to three times the space.
`--catalogurl` Software Update catalog URL used by the tool. Defaults to the default softwareupdate catalog for the current OS if you run this tool under macOS 10.13-10.15.x.
`--seedprogram SEEDPROGRAMNAME` Attempt to find and use the Seed catalog for the current OS. Use `installinstallmacos.py --help` to see the valid SeedProgram names for the current OS.
`--workdir` Path to working directory on a volume with over 10G of available space. Defaults to current working directory.
`--compress` Output a read-only compressed disk image with the Install macOS app at the root. This is slower and requires much more working disk space than the default, but the end product is more useful with tools like Munki and Imagr.
`--ignore-cache` Ignore any previously cached files. All needed files will be re-downloaded from the softwareupdate server.
