Q:

What does %Path% mean at the end of PATH?

My PATH on Windows looks like this:

C:>echo %PATH%
  C:\WINDOWS\system32;C:\WINDOWS;C:\dwimperl\perl\bin;C:\dwimperl\perl\site\bin;C:\dwimperl\c\bin;%Path%  

What does %Path% mean at the end of the PATH?
Does it have to be at the end? I want to concatenate other directories in the R script and I would naturally put them at the end of the PATH (behind %Path%).

A:

That looks like a mistake in some other script / batch command where a literal
%PATH% was appended to the PATH instead of the contents of the PATH
environment variable. This would have happened if the PATH wasn’t already set
when the script set the PATH environment variable. If an environment variable
isn’t actually set, %PATH% expands to a literal %PATH%.
Unset the PATH environment variable:
C:\>set PATH=

See what %PATH% expands to:
C:\>echo %PATH%
%PATH%

Attempt to prepend a directory to the current PATH (which isn't actually set):
C:\>set PATH=C:\Perl;%PATH%

C:\>echo %PATH%

C:\Perl;%PATH%

