I'm trying to fix the appveyor setup for Boost.GIL, where I need to create a `user-config.jam` file with entries for third-party libraries libjpeg, libpng, libz, and libtiff.

While this isn't a problem with bash on travis-ci, I have a hard time doing the equivalent with appveyor, presumably because I'm unable to work out how this is spelled with cmd.exe or the PowerShell.

Here is my appveyor script:


and here is the error this results in:


I'm sure I'm not the first one to attempt to do this (i.e., create a custom user-config.jam on appveyor). Can someone see what I'm doing wrong ?



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