Git ahead/Behind numbers in the prompt - Copied from http://blogs.atlassian.com/2013/07/git-upstreams-forks/?utm_source=2013-08-newsletter&utm_medium=email&utm_campaign=atlassian-newsletter

ahead_behind.sh

# Use it like `export PS1="\h:\w[\$(ahead_behind)]$"`
function ahead_behind {
    curr_branch=$(git rev-parse --abbrev-ref HEAD);
    curr_remote=$(git config branch.$curr_branch.remote);
    curr_merge_branch=$(git config branch.$curr_branch.merge | cut -d / -f 3);
    git rev-list --left-right --count $curr_branch...$curr_remote/$curr_merge_branch | tr -s '\t' '|';
}