Sample tutorial for dealing with a "git pull" error

gistfile1.txt

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 "metadata": {
  "name": "git_wont_pull"
 },
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 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "What to do when git won't pull"
     ]
    },
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Monday"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Say you've got a repository on your local computer that you sync to a remote repository that your whole lab shares.\n",
      "\n",
      "You do some work on Monday, and push it to the repository.  "
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Here's your (correct) workflow for Monday."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "First, you sync with the remote repository"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "ls\n",
      "git pull"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "README.md\n",
        "Already up-to-date.\n"
       ]
      }
     ],
     "prompt_number": 34
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Then, you create a file and add it to be committed."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "touch nowimworking.txt\n",
      "echo \"Look at me.  Work work work\" > nowimworking.txt\n",
      "\n",
      "git add -A\n",
      "git status"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "# On branch master\n",
        "# Changes to be committed:\n",
        "#   (use \"git reset HEAD <file>...\" to unstage)\n",
        "#\n",
        "#\tnew file:   nowimworking.txt\n",
        "#\n"
       ]
      }
     ],
     "prompt_number": 35
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now, you commit and push this to the repository.  This is the right way of doing things!  Good job on Monday!"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "git commit -m \"I've committed all of this work!\"\n",
      "git push"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[master 6862b4b] I've committed all of this work!\n",
        " 1 file changed, 1 insertion(+)\n",
        " create mode 100644 nowimworking.txt\n"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stderr",
       "text": [
        "To https://github.com/choldgraf/git_wont_pull\n",
        "   3d93d42..6862b4b  master -> master\n"
       ]
      }
     ],
     "prompt_number": 36
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "While you were sleeping, your co-worker is busy at work!"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Tuesday morning"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Then, you arrive on Tuesday morning, and realize that you didn't name the file correctly..."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "so you change it, and you also change the text"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "echo \"Whoops, I forgot to change something important\" > nowimworking.txt\n",
      "cat nowimworking.txt"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Whoops, I forgot to change something important\n"
       ]
      }
     ],
     "prompt_number": 37
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "then you realize \"whoops, I forgot to synchronize my code to the repository\".  \n",
      "\n",
      "This might be important because another lab member was changing some code the night before."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "You stop writing code, move to the command line, and quickly try a git pull."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "git pull"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Updating 6862b4b..3984193\n"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stderr",
       "text": [
        "From https://github.com/choldgraf/git_wont_pull\n",
        "   6862b4b..3984193  master     -> origin/master\n",
        "error: Your local changes to the following files would be overwritten by merge:\n",
        "\tnowimworking.txt\n",
        "Please, commit your changes or stash them before you can merge.\n",
        "Aborting\n"
       ]
      }
     ],
     "prompt_number": 38
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Whoops!  You just broke git!"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "So, what just happened?"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Ultimately, git wants to make sure that nobody unintentionally overwrites their own work or the work of others.  "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " In this case, person A made changes to their local repository, but they didn't sync person B's changes first.\n",
      "    \n",
      " So, if person A had sync'ed, it would have overwritten their own changes."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " Git assumes you don't want this to happen, so it returns an error rather than overwriting stuff for you."
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "How do get around this?"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "It's important to know that whenever you \"git pull\", git is really doing two things:"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "A \"git fetch\", which retrieves the latest copy of the remote repository and stores it somewhere to be used later"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "A \"git merge\", which tries to merge that fetched repository with the branch you're currently on"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "In this case, the \"merge\" noted that there were conflicts between the remote repository and your own"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Luckily, fixing this problem is as easy as performing the abovementioned commands <em>independently</em> of one another"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "So here's how you fix this:"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "First we fetch the latest copy of the remote repository.  Note that this copy will be called \"origin/master\", corresponding to the \"master\" branch of the remote repository referenced by \"origin\""
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "git fetch origin"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 39
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now we need to commit our changes so that git can properly compare them"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "git add -A\n",
      "git commit -m \"I'm committing my changes so that I can merge with the remote repository\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stderr",
       "text": [
        "usage: git diff [--no-index] <path> <path>\n"
       ]
      }
     ],
     "prompt_number": 27
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now, try to merge...a conflict will come up, so we will use a mergetool"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "git merge origin/master\n",
      "git mergetool"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now, we have the merge completed, we need only commit the merge and push to the repository"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "git commit -m \"Successfully merged\"\n",
      "git push"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Note - this often means you'll need to use something like a mergetool.  I'm going to assume you know how to use one here."
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Now, your local repository is synced with the remote repo, and we can continue our work."
     ]
    },
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "The End"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " "
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      " "
     ]
    },
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "To delete the git repository and re-initialize a new one!"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "rm -r myRepo/\n",
      "rm -r ../person2/myRepo2/"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 31
    },
    {
     "cell_type": "heading",
     "level": 4,
     "metadata": {},
     "source": [
      "Create my repo"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "git clone https://github.com/choldgraf/git_wont_pull myRepo\n",
      "cd myRepo\n",
      "git status"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Cloning into 'myRepo'...\n",
        "# On branch master\n",
        "nothing to commit (working directory clean)\n"
       ]
      }
     ],
     "prompt_number": 32
    },
    {
     "cell_type": "heading",
     "level": 4,
     "metadata": {},
     "source": [
      "Create the second (your friend's) repo"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "git clone http://github.com/choldgraf/git_wont_pull ../person2/myRepo2\n",
      "cd ../person2/myRepo2\n",
      "git status"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "Cloning into '../person2/myRepo2'...\n",
        "# On branch master\n",
        "nothing to commit (working directory clean)\n"
       ]
      }
     ],
     "prompt_number": 33
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "This totally resets the git repository back to its original commit"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%bash\n",
      "cd myRepo/\n",
      "git reset --hard 3d93d42d5230ac50677d847350c3c455fd792c94\n",
      "git push -f"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "HEAD is now at 3d93d42 first commit\n"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stderr",
       "text": [
        "To https://github.com/choldgraf/git_wont_pull\n",
        " + c42e00a...3d93d42 master -> master (forced update)\n"
       ]
      }
     ],
     "prompt_number": 28
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}