In pkgIndex.tcl files, a variable named dir is guaranteed to be available and hold the name of the directory in which that file resides. It is not guaranteed that this is a global variable, nor need it be related to what [file dirname [info script]]] returns (i.e., the latter can be quite irrelevant for this situation).
This information is used to construct package ifneeded scripts for the packages defined, as these typically source or load the file in which the package implementation resides. It is then important that the value of dir, or some value derived from this, gets embedded into the script Examples:
package ifneeded pureTclPackage 1.0 [list source [file join $dir purePkg.tcl]] package ifneeded compiledPackage 1.0 [list load [file join $dir compiledPkg[info sharedlibextension]]] package ifneeded mixedPackage 1.0 "[list source [file join $dir mixedPkg.tcl]] ; [list load [file join $dir mixedPkg[info sharedlibextension]]]"
Results can be
% package ifneeded pureTclPackage 1.0 source /usr/local/lib/tcltk/misc/purePkg.tcl % package ifneeded compiledPackage 1.0 load /usr/local/lib/tcltk/misc/compiledPkg.so % package ifneeded mixedPackage 1.0 source /usr/local/lib/tcltk/misc/mixedPkg.tcl ; load /usr/local/lib/tcltk/misc/mixedPkg.so