How to fix '.' is not an internal or external command error

Just leave out the "dot-slash" ./:

D:\Gesture Recognition\Gesture Recognition\Debug>"Gesture Recognition.exe"

Though, if you wanted to, you could use .\ and it would work.

D:\Gesture Recognition\Gesture Recognition\Debug>.\"Gesture Recognition.exe"

I got exactly the same error in Windows 8 while trying to export decision tree digraph using tree.export_graphviz! Then I installed GraphViz from this link. And then I followed the below steps which resolved my issue:

• Right click on My PC >> click on "Change Settings" under "Computer name, domain, and workgroup settings"
• It will open the System Properties window; Goto 'Advanced' tab >> click on 'Environment Variables' >> Under "System Variables" >> select 'Path' and click on 'Edit' >> In 'Variable Value' field, put a semicolon (;) at the end of existing value and then include the path of its installation folder (e.g. ;C:\Program Files (x86)\Graphviz2.38\bin) >> Click on 'Ok' >> 'Ok' >> 'Ok'
• Restart your PC as environment variables are changed

Replacing forward(/) slash with backward(\) slash will do the job. The folder separator in Windows is \ not /