How can I find out if I have Xcode commandline tools installed?

if you want to know the install version of Xcode as well as Swift language current version:

Use below simple command by using Terminal:

1. To get install Xcode Version

 xcodebuild -version

2. To get install Swift language Version

swift --version

/usr/bin/xcodebuild -version

will give you the xcode version, run it via Terminal command

This command allows you to retrieve Xcode version when having only the CommandLineTools version installed:

pkgutil --pkg-info=com.apple.pkg.CLTools_Executables | grep version

As per this answer to "Determine xcode command line tools version" on Ask Different

Notes:

• Confirmed working on maxOS Sierra and Big Sur.
• When only CommandLineTools is install without Xcode, using xcodebuild returns the following error:

# /usr/bin/xcodebuild -version
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

First of all, be sure that you have downloaded it or not. Open up your terminal application, and enter $ gcc if you have not installed it you will get an alert. You can verify that you have installed it by

$ xcode-select -p
/Library/Developer/CommandLineTools

And to be sure then enter $ gcc --version

You can read more about the process here: Xcode command line tools for Mavericks