use Cwd;
$dir = cwd;
use Cwd;
$dir = getcwd;
use Cwd;
$dir = fastgetcwd;
use Cwd 'chdir';
chdir "/tmp";
print $ENV{'PWD'};
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.