# colapse /./ and /.$ 
1 while ($file =~ s%/\.(/|$)%$1%g);

# colapse /dir/../ and /dir/..$ 
# ignore /../../ and /../..$
1 while ($file =~ s%/[^/]+/(?<!/\.\./)\.\.(/|$)%$1%g);

# remove ^dir/../ and ^dir/../
# ignore ^../../ and ^../..
1 while ($file =~ s%^[^/]+/(?<!^\.\./)\.\.(/|$)%%);

# colapse ^/../ to /
1 while ($file =~ s%^/\.\./%/%);

# expand null to .
$file =~ s%^$%.%;