Sometime I want to inspect software repositories. However, I don't want my machine to actually install anything from it.
To do so, I made a small bash function that both adds the repository and pins it to priority -1, telling apt to never install anything from it (unless manually told to).
The files created in the process are printed to screen so they can be easily deleted.

#Usage:   add-repository-for-inspection NAME REPOINFO
#Example: add-repository-for-inspection wheezy-backports wheezy-backports main

function add-repository-for-inspection
 shift 1
 # Add repository
 echo "deb $REPO" | sudo tee /etc/apt/sources.list.d/$NAME.list >/dev/null && echo "/etc/apt/sources.list.d/$NAME.list"
 echo -e "Package: *\nPin: release a=$RELEASE\nPin-Priority: -1" | sudo tee /etc/apt/preferences.d/$NAME >/dev/null && echo "/etc/apt/preferences.d/$NAME"

Note: It's still best to remove the files and apt-get update immediately after checking.

For instance, I can check for alternative versions of XBMC in wheezy-backports without risking accidental installations:

FILES=$(add-repository-for-inspection wheezy-backports wheezy-backports main) && sudo apt-get update &>/dev/null && apt-cache policy xbmc && sudo rm -f $FILES && sudo apt-get update &>/dev/null