Quick Look is a feature I use almost every single day, introduced by Apple with 10.5 Leopard in October 2007. It allows you to highlight a file or directory, press the spacebar, and review a pop-up window “preview” of your selection. This is particularly useful when you need a snippet of information from a PDF or text document and don’t have the time or resources to launch another program just to obtain that snippet.
By default, you can only look at information; you cannot copy and paste anything. With the following Terminal command, however, you will be able to copy and paste to your heart’s content within Quick Look:
defaults write com.apple.finder QLEnableTextSelection -bool true
Then execute:
killall Finder
From now on, you’ll be able to copy and paste any text in Quick Look. If you wish to turn this off, execute the commands with "-bool false" instead.