How do I check the downloaded image of R to ensure it has not been tampered with or corrupted during the mirroring process?

Question

When I recently downloaded the latest version of R to a new MacBook Pro, the web page at the CRAN at UC Berkeley for MAC OS said to "check the MD5 checksum of the downloaded image to ensure that it has not been tampered with or corrupted during the mirroring process."

It says, "For example, type md5 R-2.13.0.pkg in the Terminal application to print the MD5 checksum for the R-2.13.0.pkg image."

The text in quotes I copied from: http://cran.cnr.berkeley.edu/ on June 27, 2011.

Answer 1

1. Open up a Terminal Window (Hit Apple Key + Space, type Terminal, hit enter)
2. When the window is ready, type: md5

3. Find the R--2.13.0.pkg file you downloaded; drag it into the terminal window. This will simply copy the file path into terminal, so you will have something like:

   chris:~ chris$ md5 /Users/chris/Downloads/R-2.13.0.pkg
   

4) Hit return, you will get back something like:

chris:~ chris$ babd21ebbc9cbe05ff713aaaa694eff7

Now just check that number against the original, which can be found on the R website in super-tiny subscript below the download link