Input password every time is annoying, here’s a tiny script that can save your time:

#!/bin/bash
cd [your git repo]
git pull "http://username:password@github.com/xxx/project/repo.git" master

or you can upgrade it into taking different branches by using arguments:

#!/bin/bash
if [ "$#" -ne 2 ]; then
  echo "Usage: $0 repo-directory $1 branch-name " >&2
  exit 1
fi
cd $0
git pull "http://username:password@github.com/xxx/project/repo.git" $1

translation: if argument number is not equal to 2, print the error message to stderr and return. Else take $0 as the repo directory and pull the branch $1.