The  s{ ([^/]+) /[.]{2}/ \1 } /$1/gx; regex only handles the 'foo/../foo' case; it does not handle something like 'foo/bar/../../baz'.

Purely as a mental exercise, a deprecated regex approach to handling repeated return to a parental directory might be something like:

>perl -wMstrict -le
"my $parent = qr{ \.\. / }xms;
 my $dir    = qr{ (?> [^/]+ /) (?<! $parent) }xms;
 print 'output:';
 for my $f (@ARGV) {
   1 while $f =~ s{ $dir $parent }{}xmsg;
   print $f
   }
"
/vobs/foo/../foo/bar/me/my/../../me/my/moo
/vobs/foo/../bar/me/my/../../ma/mo/moo
/vobs/x/y/z/../../../x/y/z/filename
/vobs/x/y/z/../../../a/b/c/filename
/a/../b/c/d/../../e/f/g/h/i/../../../j/k/l/m/n/o/p/../../../../q
output:
/vobs/foo/bar/me/my/moo
/vobs/bar/ma/mo/moo
/vobs/x/y/z/filename
/vobs/a/b/c/filename
/b/e/f/j/k/l/q
[download]

However, this falls into the class of Stupid Regex Tricks because:

• I doubt it covers all possible variations of *nix path;
• Even if it covers all such variations (or the subset thereof that the OPer is interested in), extensive testing would be needed to verify this;
• It does not handle symlinks (see Re^3: 2 substitution problems below);
• It is not portable to other file systems;
• And finally, I'm sure there are a few other objections one could think of given a little time.

As Amphiaraus said, the preferred solution would be some module like Cwd that would overcome all these objections.

Update: Added symlink objection to list of regex solution objections per parv.

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