QuickLook scans file contents before you open those files. Usually this just lets you view a file quickly. But you can also use this same technology from the command line to bring about a change to the Finder without actually opening a file. To access QuickLook from the command line, use qlmanage.

qlmanage -p ~/Desktop/MyTowel42.pdf

—Charles Edge

I highly recommend adding an alias to your either your .bashrc or .bash_profile. This will make accessing the command faster, plus you have the added benefit of not seeing all the debug information in your current terminal session.

Below is the command I use:

ql () { qlmanage -p "$*" >& /dev/null; }

Now you can preview a file from Terminal by using ql plus the path to a file.