Wherever the script registered with [package unknown]
is programmed to look.  That is, this is completely
application configurable.


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[MG] Slightly related, you can check which files were loaded/sourced by a [package] by using [package ifneeded]:

 (User) 1 % package require Tk
 8.4
 (User) 2 % package ifneeded Tk 8.4
 load {C:/Program Files/Tcl/lib/tk8.4/../../bin/tk84.dll} Tk

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Thanks to a pointer from [DGP] on Tcl chat about the use of package unknown, here is a proc to return the command that will be used to load a package ''without actually loading it''. If you do not mind the package being loaded, you could just do ''package ifneeded foo [package require foo]'' instead.

======
proc get_package_load_command {name} {
    # Get the command to load a package without actually loading the package
    #
    # package ifneeded can return us the command to load a package but
    # it needs a version number. package versions will give us that
    set versions [package versions $name]
    if {[llength $versions] == 0} {
        # We do not know about this package yet. Invoke package unknown
        # to search
        {*}[package unknown] $name
        # Check again if we found anything
        set versions [package versions $name]
        if {[llength $versions] == 0} {
            error "Could not find package $name"
        }
    }
    return [package ifneeded $name [lindex $versions 0]]
}
======


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[Category Package] [Category Introspection]