This is a variable found in Unix interactive tclsh.
Detail on this page the purpose for which it is used.
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'''[DGP]''' 2003-05-14: tcl_libPath has only one documented use.
It holds a list of directories, and the C-level '''encoding''' documentation
says that if you add another directory to that list, then the
new directory will be searched for ''*.enc'' files that hold
additional encodings for Tcl to recognize.

But... that documentation is false.  This means of extending
the encoding search path does not work.  Never has.  See
Tcl Bug 463190.  Starting with Tcl 8.5, the [[encoding dirs]]
command is the facility that actually works.

So,... Tcl programmers should just pretend ''tcl_libPath''
does not exist.  It cannot be used for anything useful.
Treat it as an internal detail of Tcl, not for your use.

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[LV] and in fact, in at least Tcl 8.5a4, the variable doesn't
appear to be found:
 
 % puts $tcl_libPath
 can't read "tcl_libPath": no such variable

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See also [tclvars] and [Tcl syntax help].
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[Category Internals]