CERNLIB Hook Description

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# CERNLIB {#cernlib-hook}

This hook sets the `CERN`, `CERN_LEVEL`, and `CERN_ROOT` environment variables. They are part of [CERNLIB's build system](https://cernlib.web.cern.ch/install/install.html), and are are needed for some programs to compile correctly.

Title: CERNLIB Hook Description

Summary

This section describes the CERNLIB hook, which sets the `CERN`, `CERN_LEVEL`, and `CERN_ROOT` environment variables. These variables are required by CERNLIB's build system and are necessary for some programs to compile properly.