gem install : 'make' is not recognized as an internal or external command,

'make' is not recognized as an internal or external command, operable program or batch file.

H:\community-buy>gem install json -v 1.8.3
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
ERROR: Error installing json:
 ERROR: Failed to build gem native extension.

C:/Ruby21-x64/bin/ruby.exe extconf.rb
creating Makefile

make "DESTDIR=" clean
'make' is not recognized as an internal or external command,
operable program or batch file.

make "DESTDIR="
'make' is not recognized as an internal or external command,
operable program or batch file.

make failed, exit code 1

Gem files will remain installed in C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/json-1.8.3 for inspection.
Results logged to C:/Ruby21-x64/lib/ruby/gems/2.1.0/extensions/x64-mingw32/2.1.0/json-1.8.3/gem_make.out

H:\community-buy>make
'make' is not recognized as an internal or external command,
operable program or batch file.

Solution

$> cd c:\ruby\DevKit
$> devkitvars.bat
then you can use "make"