Here is another Cwd consideration. If the directory is a mounted filesystem, getcwd() (as the owner of the mounted filesystem) may return undefined if the owner has insufficient access to the underlying mount-point even if he has full access to the mounted filesystem.

For example:

                #get group
                $groups =  `/usr/bin/id -G $username`;
                chomp $groups;

                # drop privileges to owner of filesystem
                $) = "$groups"; #setegid
                $> = $uid; #seteuid

                $currentdir = Cwd::getcwd();
                my $lasterr = $!;

                if (not defined $currentdir) {
                    print "getcwd() failed : @_\n";
                } else {
                    print "getcwd() for $over is OK.";
                }
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A command like tar will usually give an error like "tar: The getwd subroutine failed. Cannot open parent directory."

This is useful to know in cases where the underlying stub directory's permissions affect programs relying on getcwd() e.g. /bin/pwd, tar etc.

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