Install Xcode command line tools on 10.7.x - 10.10.x. Tested on 10.7.5, 10.8.5, 10.9.5 and 10.10.2.

gistfile1.sh

#!/bin/bash

# Installing the Xcode command line tools on 10.7.x or higher

osx_vers=$(sw_vers -productVersion | awk -F "." '{print $2}')
cmd_line_tools_temp_file="/tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress"

# Installing the latest Xcode command line tools on 10.9.x or higher

if [[ "$osx_vers" -ge 9 ]]; then

	# Create the placeholder file which is checked by the softwareupdate tool 
	# before allowing the installation of the Xcode command line tools.

	touch "$cmd_line_tools_temp_file"

	# Find the last listed update in the Software Update feed with "Command Line Tools" in the name

	cmd_line_tools=$(softwareupdate -l | awk '/\*\ Command Line Tools/ { $1=$1;print }' | tail -1 | sed 's/^[[ \t]]*//;s/[[ \t]]*$//;s/*//' | cut -c 2-)

	#Install the command line tools

	softwareupdate -i "$cmd_line_tools" -v

	# Remove the temp file

	if [[ -f "$cmd_line_tools_temp_file" ]]; then
	  rm "$cmd_line_tools_temp_file"
	fi
fi

# Installing the latest Xcode command line tools on 10.7.x and 10.8.x

# on 10.7/10.8, instead of using the software update feed, the command line tools are downloaded
# instead from public download URLs, which can be found in the dvtdownloadableindex:
# https://devimages.apple.com.edgekey.net/downloads/xcode/simulators/index-3905972D-B609-49CE-8D06-51ADC78E07BC.dvtdownloadableindex

if [[ "$osx_vers" -eq 7 ]] || [[ "$osx_vers" -eq 8 ]]; then

	if [[ "$osx_vers" -eq 7 ]]; then
		DMGURL=http://devimages.apple.com/downloads/xcode/command_line_tools_for_xcode_os_x_lion_april_2013.dmg
	fi

	if [[ "$osx_vers" -eq 8 ]]; then
		 DMGURL=http://devimages.apple.com/downloads/xcode/command_line_tools_for_osx_mountain_lion_april_2014.dmg
	fi

		TOOLS=cltools.dmg
		curl "$DMGURL" -o "$TOOLS"
		TMPMOUNT=`/usr/bin/mktemp -d /tmp/clitools.XXXX`
		hdiutil attach "$TOOLS" -mountpoint "$TMPMOUNT" -nobrowse
		# The "-allowUntrusted" flag has been added to the installer
		# command to accomodate for now-expired certificates used
		# to sign the downloaded command line tools.
		installer -allowUntrusted -pkg "$(find $TMPMOUNT -name '*.mpkg')" -target /
		hdiutil detach "$TMPMOUNT"
		rm -rf "$TMPMOUNT"
		rm "$TOOLS"
fi

exit 0

This is awesome. The only thing I could recommend is change installer -allowUntrusted -pkg... to sudo installer -allowUntrusted -pkg... and it works great. And if you want to detect if Xcode CL Tools is installed then just run pkgutil --pkgs | grep com.apple | grep CL | grep Tools (I have tested this on 10.7.x, 10.8.x, 10.9.x, 10.10.x, and 10.11.x).

Fantastically useful script. I noticed a problem running the script on MacOS Sierra unfortunately. Softwareupdate may have changed.
softwareupdate: invalid option -- v

We found dropping the -v from the script makes it work for our Sierra deployments now.

Thanks so much for this! Is there an xcode-select --switch required afterwards?

Awesome and thank you. Was going to do it by myself withxcode-select --install because in the majority of use cases the person who's in need of CLI tools has Xcode installed already and this command is the most straightforward approach available. However, to execute it Xcode has to be version 5 or newer: in Xcode 4.x.x for Lion and Mountain Lion there's no --install so I had to figure out how to install them via Terminal for my script. You left me standing and your approach is superseding those commands to install CLI tools that are based just on the version of macOS and Xcode. Thank you. I'll credit you as the one my script was derived from.