Tcl workers often first encounter special keywords when confronted with a situation where the same application behaves differently for two different users/hosts/...
For example, distinct auto_path-s can lead to loading of subtly different packages, which ...

[[More motivation.]]  "[tclvars]" covers a different but related territory, that of particular variables (as opposed to files or commands) that influence Tcl.










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auto_path  [[overloaded since 7.5--an understandable historical mistake]]


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pkgIndex.tcl:  [package] currently searches [auto_path] for files named "pkgIndex.tcl".
More precisely, [[... [tclPkgUnknown] ...]]











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.tclshrc

Note that the '''~/.tclshrc''' file ('''~/tclshrc.tcl''' on Windows)
are special values given by '''tclsh''' to the global variable
tcl_rcFileName.
The value of $::tcl_rcFileName is only special to applications like '''tclsh''' that call ''Tcl_Main()'', not to Tcl itself.






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.Xdefaults  [[... [option] ... ]]






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TCLLIBPATH























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[[ "[Tcl syntax help]" touches on some of same topics.]]