Quick Look on OS X is a great feature for previewing the images, sounds, videos and text files. However, for some reason Apple has chosen not to allow selection in Quick Look, you can’t click and drag to select the content. We can fix this, and here is how.
To enable the text selection, type the following in your Terminal window:
defaults write com.apple.finder QLEnableTextSelection -bool TRUE && killall Finder
Obviously, this will also restart your Finder, so make sure you aren’t doing anything important.
To deactivate the feature for some reason, use the following:
defaults delete com.apple.finder QLEnableTextSelection && killall Finder