Sep 1, 2011 — by: Karl Johnson
Categories: Mac Applications, Terminal

Few people have used the Terminal application and even fewer understand it. The goal of this new series of articles at T-GAAP will teach Mac users to use the Terminal and its commands to change the way the Mac OS runs.

The Terminal gives users access to some pretty powerful tools inside the Mac OS. These tools allow you to get under the hood of the OS engine in a new way. The first article will give just a taste of the power inside the Terminal application.

Grab is a tiny application that can take screen grabs or pictures of what one sees on the screen. Apple gives some default shortcuts to access Grab without even launching the application. Use command+shift+4 to grab a selection of the screen and save it to the Desktop. The problem with Grab is that the default file format is PNG. While this is a nice file format, JPG is the dominant picture format for most people. There is no way to change this default file format within Grab, but there is a way to change it with the Terminal application.

The first step is to launch Terminal, which is in the Applications/Utilities folder. Once the Terminal is launched, copy and paste the following information into the Terminal command prompt.

defaults write type jpg

This command tells Apple's screen capture utility to change it's default file format. The last word is the command that defines the file format, which in this case is jpg. Other file formats include pdf, tif, and psd. To change it back to png, copy and paste the following in the Terminal.

defaults write type png

Once it has been pasted into command in the Terminal, hit the enter key to run the command. The computer may need to be restarted in order to activate the new default.

This gives just a taste of the power inside the Terminal. Future articles will go into the basic usage of the Terminal, more commands to modify the Mac OS, and other powerful utilities already included in the Mac OS.


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  1. nauval2007 ~ Jun. 21, 2012 @ 6:15 pm

    Oops.. I thought you will tell me how to change default file format. This terminal command just change default format if I use cmd+shift+4 but not for grab application. #
  2. Mark ~ Feb. 23, 2013 @ 10:36 pm

    This does not work. #
  3. Sishy ~ Mar. 12, 2013 @ 9:28 pm

    I guess this doesn't work for OS 10.8.2 becuase it sure as heck isn't working for me. #
  4. Lorraine ~ Apr. 28, 2014 @ 6:04 pm

    The author is confusing the application called Grab and taking a regular screenshot. These instructions will NOT affect Grab, the application. They will only change the screenshot capture defaults from PNG to JPG. In fact, Grab is so useless since its default produces TIFF files, so taking JPG screenshots is so much faster and easier (default saves the screenshots to the desktop but you can change that too (see below). To take a screenshot: Command-Shift-3: whole screen Command-Shift-4, then select an area Command-Shift-4, then space, then click a window: Take a screenshot of a window To change the default folder for screenshots, launch Terminal and type: defaults write location /path/ For example: defaults write location ~/Downloads/ Hit enter, then type: killall SystemUIServer #

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