Xcode is not currently available from the Software Update server

If you are trying this on a latest Mac OS X Mavericks, command line tools come with the Xcode 5.x

So make sure you have installed & updated Xcode to latest

after which make sure Xcode command line tools is pointed correctly using this command

xcode-select -p

Which might show some path like

/Applications/Xcode.app/Contents/Developer

Change the path to correct path using the switch command:

sudo xcode-select --switch /Library/Developer/CommandLineTools/

this should help you set it to correct path, after which you can use the same above command -p to check if it is set correctly

You can download the command line tools for OS X Mavericks manually from here:

For OSX 10.11 or more you can download from here https://developer.apple.com/download/more/.

(The link in the accepted answer doesn't display command line tools for El Capitan (OSX 10.11))

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