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OS X Hidden Treasures: Quick Look

by Adam C. Engst and Josh Centers

OS X is full of useful little features that are easy to miss or forget about, such as services, which we covered in “OS X Hidden Treasures: Services [1]” (5 February 2016). Another easily overlooked feature in OS X is Quick Look, introduced in Mac OS X 10.5 Leopard back in 2009.

Quick Look offers a fast preview of what’s inside a file, most notably in the Finder and third-party file transfer apps. It works with many common file types, such as text files, images, audio, video, PDFs, Microsoft Office files, and even fonts (here’s a larger list of supported file types [2]).

We’ll explain how to use Quick Look, in which apps you can use it, and how to use it from the command line (which is also helpful for troubleshooting). Then we’ll share some of our favorite Quick Look plug-ins to extend Quick Look’s capabilities and make it even more useful.

(One quick internal note. If you’re reading this on our Web site, click any image to zoom it to a better size; click it again to shrink it down. It’s not Quick Look, but it’s not far off, and some reader comments have indicated that people don’t realize this is how our site works.)

Basic Quick Look Usage -- To invoke Quick Look in the Finder, select a file and choose File > Quick Look “filename” (Command-Y). Better yet, just click a file and press the Space bar. The screenshot below shows Quick Look displaying a picture of an Apple Watch Edition.

[image link] [3]

With Quick Look open, you can click Open with App to open the file in its default app. You can also click the Share button in the upper right to send the file to another app or service without fully opening it. If the file you’re previewing with Quick Look has multiple pages, you’ll see thumbnails on the right that you can scroll through using your mouse or trackpad, or by using the Page Up/Page Down keys (on a laptop, use Fn-Up Arrow and Fn-Down Arrow). Although Quick Look windows generally open to a useful size, you can resize the window by dragging any edge. To close Quick Look, press the Space bar or Command-Y again, press Escape, or click the window’s close button in the upper left.

[image link] [4]

If you select multiple files before invoking Quick Look, you can use the Left and Right arrow keys to cycle through your selections; there are also forward and back buttons that appear in the top left of the Quick Look window. Next to those buttons is a thumbnail button that displays the selected files in a grid of thumbnails. Click any thumbnail to focus on just that item.

[image link] [5]

[image link] [6]

You can also use Quick Look to scan through the contents of a folder. While Quick Look is open, use the arrow keys to display other files in the same folder — how you navigate among the files depends on the Finder window’s view. Using Quick Look and the Up and Down arrow keys can be a great way to browse pictures in a folder in List view. You can continue to interact with the Finder while using Quick Look, which means you can delete an unwanted file by pressing Command-Delete while previewing it.

One interesting use of this capability is that you can use Quick Look to examine files in the Trash, which can’t otherwise be opened while they remain in the Trash. So if you want to recover a particular image among a bunch that you’ve trashed, Quick Look is a fast way to figure out which one to pull out. Similarly, you can use Quick Look within Time Machine to preview file versions before restoring them.

Certain file types offer special controls. If you open an image that’s larger than the Quick Look window, press the Option key to expand the image to its original size and use the mouse to pan around in the expanded image. Plus, when using Quick Look to preview video and audio files, you see mute and play/pause buttons, along with a scrubbable timeline.

[image link] [7]

Want to focus on an image without the distraction of your desktop? Select a file and press Option-Space (or Command-Option-Y) to open the Quick Look view in full-screen view. You can also enter full-screen view by clicking the zoom button in the upper left (to the right of the close button) while viewing a file in a regular Quick Look window.

One final tip. Quick Look also works in Open dialogs, so you can select any file and press the Space bar to see the preview. You can even select multiple files and preview them just as though you had selected them in the Finder. The only caveat is that the Open with App button does not appear.

Quick Look Outside the Finder -- Quick Look isn’t limited to the Finder. The main additional place you’ll find it is in file transfer apps like Fetch, Transmit, and Cyberduck. In those apps, Quick Look is usually invoked in exactly the same way as in the Finder, with a click to select a file and then a press of the Space bar.

[image link] [8]

However, various other OS X apps, including Mail and Messages, take advantage of Quick Look as well. In Mail, you can use Quick Look on attachments by clicking the paperclip button (which appears when you move the cursor to the message header area) and choosing Quick Look. In Messages, you can view all the attachments in a conversation by choosing File > Quick Look — it’s like previewing multiple files in the Finder with Quick Look, so you can navigate through them with arrow keys. Alternatively, double-click an attachment, select it and press the Space bar, or use a three-finger trackpad tap.

[image link] [9]

Safari, Mail, and Messages also let you summon a preview of a Web link with a three-finger tap on the trackpad (sorry, mouse users!). This may not be Quick Look behind the scenes, but it’s conceptually similar. If it doesn’t work for you, enable Look Up & Data Detectors in System Preferences > Trackpad > Point & Click.

Quick Look from the Command Line -- If you prefer the command line for browsing, you can use Quick Look from Terminal with the command qlmanage -p filename. That’s handy for a quick glance into any file that’s not straight text and thus not viewable with the likes of less and tail. It’s a little fussy — it displays a bunch of debug messages and you have to close the Quick Look preview or press Control-C to quit the process — but it’s handy if you don’t want to switch back out to the Finder to look inside a file.

[image link] [10]

The qlmanage -m command is also useful, since it displays all the loaded Quick Look plug-ins and may alert you to the existence of Quick Look support in apps you hadn’t realized supported Quick Look (DEVONthink! Evernote!). Since Quick Look plug-ins can conflict with one another (we haven’t yet figured out what determines loading order), qlmanage -m can help you determine which app has precedence. To suss out who was managing EPUB support in Quick Look (see below), we used qlmanage -m | grep epub, which filtered just the EPUB-related lines out of the full report.

Another reason to use the qlmanage command is for paranoid security reasons. Whenever Quick Look is invoked, OS X creates a cache of the thumbnail data for future use, even if the file previewed was on an external drive. To prevent an attacker (with physical access, of course) from spelunking through the thumbnail cache, you can reset it with the command qlmanage -r cache. It’s not a concern for most people, but secret agents should take note.

There’s a bug in Quick Look that fails to release previewed files right away. So if you preview a file with Quick Look, send it to the Trash, and immediately try to empty the Trash, the Finder won’t delete that file, claiming that it’s “in use.” The solution is either to wait a while for Quick Look to let go of the file, or to reset Quick Look with qlmanage -r and try again.

Finally, if you’re using a version of OS X prior to OS X 10.11 El Capitan, you can use the following Terminal command to enable copying text from the Quick Look window. Unfortunately, Apple decided to disable this option in El Capitan. Boo!

defaults write QLEnableTextSelection -bool TRUE; killall Finder

Extend Quick Look with Plug-ins -- Quick Look supports a number of file types out of the box, but far from all of them. Thankfully, Apple created a plug-in interface for Quick Look so that developers could expand its capabilities, even without a companion app.

We’ve found a number of useful Quick Look plug-ins, but before we share that list, you need to know how to install them. All standalone Quick Look plug-ins are .qlgenerator files that need to live in /Library/QuickLook (if you want the plug-in to be accessible to all users on your Mac) or in ~/Library/QuickLook (if only your user needs to be able to use it). Some Quick Look plug-ins are distributed as package files that you double-click to install in one of those locations. But most are just bare .qlgenerator files that need to be moved to a Library folder manually. To install them in your user Library folder, in the Finder, press Option and choose Go > Library. Then open the QuickLook folder (create it if necessary, noting that the folder name doesn’t have a space between the two words). Drag .qlgenerator files into this folder.

After installing a new Quick Look plug-in, OS X should notice and load it automatically, but if the plug-in doesn’t seem to work, you may need to refresh the Quick Look engine. A restart is easy, but you can instead either log out and back in or Control-Option-click the Finder icon in the Dock and choose Relaunch. Or, if you’re in Terminal, type qlmanage -r and press Return.

With that out of the way, here are some of our favorite Quick Look plug-ins:

For even more Quick Look goodness, check out the QuickLook Plugins List [29], which is the best centralized repository of Quick Look plug-ins.

Quick Look is easy to master, and once you get in the habit of using it, you’ll be all the more productive on your Mac. Let us know in the comments if you have any other Quick Look tricks or plug-ins that you find useful!