It looks like Win32::FileOp exports the method Substed, which if invoked on your drive letter will tell you whether it's substed somewhere else, or where the drive mapping leads if it's a network mapped drive. The output syntax is a little odd (in particular it uses windows-native \ for directory separation rather than perl-standard /), but with a little work it should get the job done. Running the following in -e from the command line:

print join(',',Substed(split(/\//,cwd)));
[download]

... yields ...

C:\>perl -MCwd -MWin32::FileOp -e "..."
,HarddiskVolume1

X:\>perl -MCwd -MWin32::FileOp -e "..."
\??\C:\temp,

Z:\>perl -MCwd -MWin32::FileOp -e "..."
\??\C:,

O:\>perl -MCwd -MWin32::FileOp -e "..."
,LanmanRedirector\;O:000000000002ef75\SOME-MACHINE\Network\Share
[download]

Note the comma in the above examples, Substed returns a list of two elements, which I joined with a comma in the output. I've substed X: to C:\temp, Z: to C:\, and O: is a network share.