/usr/local/bin/git-pushu (assumes that you always like your `origin` remote)

git-pushu.sh

#!/bin/bash

if ( git status | grep "origin" -q ); then
  git push $@
else
  branch_name="$(git symbolic-ref HEAD 2>/dev/null)"
  git push --set-upstream origin "${branch_name##refs/heads/}"
  git push $@
fi