#! perl -slw
use strict;

sub sanitizeDir {
	require Cwd;
	my( $path ) = @_;
	my( $cwd ) = Cwd::getcwd() =~ m[^(.*)$];
	return unless do{ local %ENV; $path =~ s[^(.*)$][$1]; chdir $path; };
	my $sanitized = Cwd::getcwd();
	chdir $cwd;
	return $sanitized =~ s[^$cwd][$cwd] ? $sanitized : ();
}

my $dubiousPath = $ARGV[0];

my $absPath = sanitizeDir( $dubiousPath );

if( defined $absPath ) {
	print 'Absolute path: ', $absPath;
}
else {
	print 'Invalid path:  ', $dubiousPath;
}

##</code><code>##

P:\test>perl -T junk.pl8 .
Absolute path: P:/test

P:\test>perl -T junk.pl8 ..
Invalid path:  ..

P:\test>perl -T junk.pl8 ./..
Invalid path:  ./..

P:\test>perl -T junk.pl8 ./../.
Invalid path:  ./../.

P:\test>perl -T junk.pl8 ./used
Absolute path: P:/test/used

P:\test>perl -T junk.pl8 ./used/..
Absolute path: P:/test

P:\test>perl -T junk.pl8 ./used/../..
Invalid path:  ./used/../..

P:\test>perl -T junk.pl8 ./used/././t/
Absolute path: P:/test/used/t

P:\test>perl -T junk.pl8 ./used/././t/../
Absolute path: P:/test/used

P:\test>perl -T junk.pl8 ./used/././t/../..
Absolute path: P:/test

P:\test>perl -T junk.pl8 ./used/././t/../.././..
Invalid path:  ./used/././t/../.././..