How To Open Two Instances Of An Application In OS X

Whether you want to look at two PDF pages side-by-side or you want two Twitter accounts open at once, sometimes OS X requires a separate instance of an application to be open. Here’s how to do it with a simple Terminal command.

Say you want to look at two PDF pages side-by-side. If they’re in the same PDF, OS X won’t let you open the PDF twice — it’ll just direct you to the first instance of the open file. The open command, however, will let you open two instances of most programs with the -n parameter. So, to open two instances of the same PDF, just double-click on the PDF to open the first instance, then run:

open -n “path/to/file.pdf”

to open the second one in Preview. Of course, replace path/to/file.pdf with the path to the file you want to open. It will open up in a new instance of Preview, with its own dock icon and everything.

This will actually work with a number of programs (not iTunes though, apparently), and if you want to do it often, Macworld suggests turning it into an Automator service. I had a bit of trouble getting Macworld’s code to work, so I tweaked it to something that worked for me, using an AppleScript. We’ve shown you how to use Automator before, so just open it up, create a new service that accepts any type of file from the Finder, and add the Run AppleScript action with the following code in the box:

on run {input, parameters}

set input1 to quoted form of POSIX path of input
do shell script “open -n ” & input1

end run

Your service should look like this (click to enlarge):

Now just save it as whatever you want (I named mine “Open in New Instance”). When you right-click on a file in the Finder, you can open it using a second instance of its corresponding application by selecting your new service.

Open Two Instances of Preview at Once [Macworld]