'''[http://core.tcl.tk/tcllib/doc/trunk/embedded/www/tcllib/files/modules/fileutil/traverse.html%|%fileutil::traverse]''', a [tcllib] module, provides utilities for traversing directory hierarchies.



** Description **

[hv]: While traversing down a directory, there are times when you encounter one
that is not accessible. While the documentation stated that the package will
ignore those directories by default. In reality, my sample script crashed.
Curious, I dug into the source code and found what might be a bug. I posted the
problem and a work-around solution on
http://stackoverflow.com/questions/17633681/how-to-handle-permission-denied-when-using-fileutiltraverse%|%StackOverflow%|%

To sum up, I used the `-prefilter` option to determine if a directory is
readbale:

======
package require fileutil::traverse

proc isAccessible {absPath} {
    return [file readable $absPath]
}

# Main
set searchDir /tmp
fileutil::traverse t $searchDir -prefilter isAccessible

puts "\nFiles in $searchDir:"
t foreach fileName {
    puts $fileName
}
======
[Mho] 2020-10-12: Just tried `fileutil::traverse T c:/users` on my windows machine.

After ~800k files I got this:

`could not read link "c:/users/matthiasu/AppData/Local/Packages/Microsoft.Microsoft3DViewer_8wekyb3d8bbwe/LocalCache": invalid argument`

Experimenting again later. Calling with an invalid (non existent) folder: the foldername itself is returned. Neither -prefilter nor -errorcmd triggered.
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