use strict;
use warnings;

#use Win32;

print 'I am ', Win32::LoginName, ' in domain ', Win32::DomainName, $/;
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In addition to the informative thread marto referred to above, which points to Win32::LoginName, knowing the domain an accounts comes from might be of interest too, especially in a bigger AD environment (forest).

Also note, that ActiveState's perl on Windows is special, with regard to the Win32 module, insofar as it distinguishes between "[CORE]" functions and others.

Those [CORE] functions are available, even without a "use Win32;" (LoginName and DomainName among them).

More information on Win32 functions is available from the cmd command line with perldoc Win32.