Cwd(3)

NNAAMMEE
       getcwd - get pathname of current working directory

SSYYNNOOPPSSIISS
           use Cwd;
           $dir = cwd;

           use Cwd;
           $dir = getcwd;

           use Cwd;
           $dir = fastgetcwd;

           use Cwd 'chdir';
           chdir "/tmp";
           print $ENV{'PWD'};

DDEESSCCRRIIPPTTIIOONN
       The getcwd() function re-implements the getcwd(3) (or
       getwd(3)) functions in Perl.

       The fastcwd() function looks the same as getcwd(), but
       runs faster.  It's also more dangerous because it might
       conceivably chdir() you out of a directory that it can't
       chdir() you back into.  If fastcwd encounters a problem it
       will return undef but will probably leave you in a
       different directory.  For a measure of extra security, if
       everything appears to have worked, the fastcwd() function
       will check that it leaves you in the same directory that
       it started in. If it has changed it will die with the
       message "Unstable directory path, current directory
       changed unexpectedly". That should never happen.

       The cwd() function looks the same as getcwd and fastgetcwd
       but is implemented using the most natural and safe form
       for the current architecture. For most systems it is
       identical to `pwd` (but without the trailing line
       terminator).

       It is recommended that cwd (or another *cwd() function) is
       used in all code to ensure portability.

       If you ask to override your chdir() built-in function,
       then your PWD environment variable will be kept up to
       date.  (See the section on Overriding Builtin Functions in
       the perlsub manpage.) Note that it will only be kept up to
       date if all packages which use chdir import it from Cwd.