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The first will add eups (the LSST package management software) to your PATH. The second will tell eups to add the CatSim code to your PATH.
Note: If you want to run the CatSim-GalSim interface which allows you to seamlessly convert CatSim catalogs into GalSim images, you should replace sims_catUtils with sims_GalSimInterface in the commands above.
Organization of Software
The software in the LSST stack is organized using the package management program EUPS. Broadly speaking, every time you install a new version of the stack using
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