Since you said "May be C:\My_Docs\Perl or C:\Perl or D:\Perl" then I will assume you are running on Windows.

The problem is that you might have more than one version installed, but Windows has a fundamental problem with that. When you type perl on the command-line (cmd.exe) it attempts to load perl.exe usings its executatble search mechanism, which is complex, but usually involves the %PATH% environment variable (use the path cmd.exe command to check).

However, when you run a perl script from the command-line, the shell uses the file association in the registry. You can check this, for example:

C:\>assoc .pl
.pl=Perl

C:\>ftype Perl
Perl="C:\Perl\bin\perl.exe" "%1" %*
[download]

In theory the %PATH% and file association might refer to different versions.
You mentioned "$Perl Script$": I'm not sure what that is but it could be the ftype? If so, make sure you enclose it in double quotes to find the location.