Quick Look is a quick preview feature developed by Apple Inc. which was introduced in its

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Mac OS X 10.5 Mac OS X Leopard (version 10.5) is the sixth software versioning, major release of macOS, Apple Inc., Apple's desktop and server operating system for Macintosh computers. Leopard was released on October 26, 2007 as the successor of Mac OS X Tig ...

Leopard. The feature was announced at the

Worldwide Developers Conference The Worldwide Developers Conference (WWDC) is an information technology conference held annually by Apple Inc. The conference is usually held at Apple Park in California. The event is usually used to showcase new software and technologies in t ...

on Jun. 11, 2007. While macOS's Finder has always had smaller previews in Get Info windows or column view, Quick Look allows users to look at the contents of a file at full or near-full size in the Finder, depending on the size of the document relative to the screen resolution. It can preview files such as

PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaS ...

, QuickTime readable media,

plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects (floating-point numbers, images, etc.). It may also include a limit ...

and RTF text documents,

iWork iWork is an office suite of applications created by Apple Inc. for its macOS and iOS operating systems, and also available cross-platform through the iCloud website. It includes the presentation application Keynote, the word processing and ...

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Keynote A keynote in public speaking is a talk that establishes a main underlying theme. In corporate or commercial settings, greater importance is attached to the delivery of a keynote speech or keynote address. The keynote establishes the framework fo ...

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) documents, ODF documents,

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Word A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...

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, and

PowerPoint Microsoft PowerPoint is a presentation program, created by Robert Gaskins and Dennis Austin at a software company named Forethought, Inc. It was released on April 20, 1987, initially for Macintosh computers only. Microsoft acquired Powe ...

) files (including

OOXML Office Open XML (also informally known as OOXML) is a zipped, XML-based file format developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents. Ecma International standardized the initial version a ...

), and RAW camera images. Quick Look can also be opened in full screen and launched from the

command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

. Additionally, multi-page documents like PowerPoint slide shows can be navigated using the slide previews at the side of the preview window. Quick Look technology is implemented throughout the Apple suite of software starting with Mac OS X 10.5, including iChat Theater, Time Machine, and Finder's Cover Flow. Quick Look APIs are available to developers via the Quick Look framework on iOS and as part of the Quartz framework on the Mac.

Supported file types by default

Since its debut, Quick Look has included a number of generators for common file types.

Plug-ins

Plug-ins can be added to Quick Look to allow previewing the content of other

file formats A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file formats ...

. Plug-ins can also be used to add additional functionality to Quick Look such as

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for

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the ...

files. To add a plug-in to Quick Look it needs to be placed in the folder /Library/QuickLook/. To activate that plug-in, either the computer needs to be restarted or Quick Look needs to be reset with the command qlmanage -r

Usage

There are multiple ways to invoke Quick Look.

Keyboard shortcuts computing, a keyboard shortcut also known as hotkey is a series of one or several keys to quickly invoke a software program or perform a preprogrammed action. This action may be part of the standard functionality of the operating system or ...

: * - * * - (open in full screen) * hold to zoom an image to actual size (Quick Look must already be open)

Command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

: qlmanage -p file Menu: * File — Quick Look ''file name''; * Context menu (right-click or -mouse click), then Quick Look ''file name''.

Caching and Forensics

Quick Look can be exploited when conducting a

forensic examination Forensic science, also known as criminalistics, is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and criminal p ...

of a computer's contents. A

thumbnail Thumbnails are reduced-size versions of pictures or videos, used to help in recognizing and organizing them, serving the same role for images as a normal text index does for words. In the age of digital images, visual search engines and imag ...

cache is created for each user in a random subfolder of /var/folders called com.apple.QuickLook.thumbnailcache. The cache contains two files; * index.sqlite which is a

SQLite SQLite (, ) is a database engine written in the C programming language. It is not a standalone app; rather, it is a library that software developers embed in their apps. As such, it belongs to the family of embedded databases. It is the mo ...

database containing two tables - files and thumbnails. ::files contains the name, path, file-identifier, and volume-identifier of each file in the database. ::thumbnails contains metadata about each thumbnail, including the file linked-to in the files table and the offset of its data contained in thumbnails.data. * thumbnails.data contains the raw

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s of the cached thumbnails. Quick Look thumbnails are stored for documents on internal disks and also for documents located on removable disks, ''including those that have been encrypted'' and can pose a significant security hole. A document may well have a number of thumbnails, each having different dimensions that can range from very large to very small. The cache can be reset by invoking the qlmanage -r cache command via a Terminal window.

References

External links

A Quick Look Plugins list for Mac OS X

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Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...