based on the contents of a .mag file being read in, assuming
compatibility with principles of open_pdks. The search paths
are not meddled with unless a file is read for which the technology
cannot be found (and a technology has not already been read, or at
least no database file exists in memory using any technology that
has already been read). If so, then variables PDK_PATH and PDK_ROOT
are searched for in both the shell environment and the local Tcl
environment. Also, if open_pdks has installed PDKs in the path
/usr/share/pdk/, then that path will be searched. If a corresponding
technology file is found, it will be loaded. If the path corresponds
to an open_pdks-style path, then the library paths in libs.ref will
also be added to the search paths for cells.
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