Emily Brewster of Merriam-Webster offers a cogent defense of “drive safe,” “take it easy” and other cases in which adverbs seem to be missing their -ly ending:
It’s not simply a matter of do-what-you-want. These words really are adverbs, they just look like their related adjective forms. A good example is “near.” It’s an adjective, a preposition and adverb — even though there is also an -ly form.
It was a near miss. [adjective]
I work near the train station. [preposition]
The deadline draws near. [adverb]
Christmas is nearly here. [adverb]
They’re all related, but you can’t use them interchangeably.
Last night, Stuart corrected something I wrote in a Kickstarter update. Instead of “look close,” he suggested “look closely.” Both work, but there’s something I really love about the flat form.
Thanks to Bryce Edmonds for the link.