QuickLook - MacOS

QuickLook is the tool that Finder uses in MacOS to provide previews of file contents when pressing space bar on a file in Finder. qlmanage is the command line tool used to administer QuickLook.

QLManage

Use qlmanage to diagnose and change QuickLook settings.

Usage: qlmanage [OPTIONS] path...
        -h              Display this help
        -r              Force reloading Generators list
        -r cache        Reset thumbnail disk cache
        -m [name ...]   Display statistics about quicklookd. Stats names:
                        * plugins       Show the generators list
                        * server        Show quicklookd life information
                        * memory        Show quicklookd memory consumption
                        * burst         Show statistics about the last burst
                        * threads       Show concurrent accesses stats
                        * other         Show other information about quicklookd
        -p              Compute previews of the documents
        -t              Compute thumbnails of the documents
        -x              Use quicklookd (remote computation)
        -i              Compute thumbnail in icon mode
        -s size         Size for the thumbnail
        -f factor       Scale factor for the thumbnail
        -F factor       Scale factor for the thumbnail, draw downscaled and compare to 1x
        -z              Display generation performance info (don't display thumbnails)
        -o dir          Output result in dir (don't display thumbnails or previews)
        -c contentType  Force the content type used for the documents
        -g generator    Force the generator to use

To find the QuickLook generator for a specific file extension:

qlmanage -m | grep "md"

To test a quicklook generator run it explicitly on a file you want to view. For example:

qlmanage -p /path/to/sample/file.ext

Unsigned QuickLook Generators

In more recent versions of MacOS (Mohave, Big Sur, etc...) new security requirements have been put in place. This means a number of older QuickLook generators are not signed and so do not work without approval. To approve the extensions you must do the following:

1. Install the QuickLook generator, e.g. brew install qlcolorcode
2. On your terminal, xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator run (using sudo if needed), replacing QLColorcode with whatever the name of the QuickLook plugin
3. Reload the QL Generator with qlmanage -r
4. Now refresh the cache qlmanage -r cache
5. Restart Finder by running killall Finder

For those wanting to cut and paste the whole lot:

brew install qlcolorcode
xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator
qlmanage -r
qlmanage -r cache
killall Finder

QuickLook Generators I use

• QLStephen - https://whomwah.github.io/qlstephen/
  This Quick Look plug-in allows you to view most text files without specific extensions (README,Makefile etc)

• QLColorCode - https://github.com/anthonygelibert/QLColorCode
  Quick Look plug-in that renders source code with syntax highlighting

• QLMarkdown - https://github.com/toland/qlmarkdown
  QLMarkdown is a simple QuickLook generator for Markdown files

brew install qlstephen qlcolorcode qlmarkdown
xattr -cr ~/Library/QuickLook/QLMarkdown.qlgenerator 
xattr -cr ~/Library/QuickLook/QLStephen.qlgenerator 
xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator
qlmanage -r
qlmanage -r cache

Adding support for unknown file types

If there is a file extension that is not being shown by any of your QuickLook extensions, you can easily add them to the list of one of the ones I showed above.

For example, to add .conf files to the QLColorCode extension do the following:

1. Find an example file of the type that you want to add to QuickLook

2. Run mdls -name kMDItemContentType followed by the file name so in my case:

   mdls -name kMDItemContentType /Users/me/wpa_supplicant.conf
   

3. Make note of the output. In my exmaple this was:

   kMDItemContentType = "dyn.ah62d4rv4ge80g55sq2"
   

4. Now you need to add the part in quotes to the QL config. So:

   nano ~/Library/QuickLook/QLColorCode.qlgenerator/Contents/Info.plist
   

   where QLColorCode is the QL generator I want to add this file to.

5. In the editor you just opened, look for three lines that look like this:

          </array>
        </dict>
      </array>
   

6. Now add a new line before those that includes the part in quotes from step #3, so:
   <string>dyn.ah62d4rv4ge80g55sq2</string>

7. Press CTRL-X and then y and Enter to save the file

8. Run

   qlmanage -r
   

9. You may need to restart Finder

   killall Finder
   

Now you can press space on the new file type and it should open in QuickLook for you.