Magallanes/Mage/Task/BuiltIn/Scm/ChangeBranch.php

<?php
class Mage_Task_BuiltIn_Scm_ChangeBranch
    extends Mage_Task_TaskAbstract
{
	protected static $startingBranch = 'master';
    private $_name = 'SCM Changing branch [built-in]';

    public function getName()
    {
        return $this->_name;
    }

    public function init()
    {
        switch ($this->getConfig()->general('scm')) {
            case 'git':
                $this->_name = 'SCM Changing branch (GIT) [built-in]';
                break;

            case 'svn':
                $this->_name = 'SCM Changing branch (Subversion) [built-in]';
                break;
        }
    }

    public function run()
    {
    	$scmConfig = $this->getConfig()->general('scm', array());
        switch ((isset($scmConfig['type']) ? $scmConfig['type'] : false)) {
            case 'git':
            	if ($this->getParameter('_changeBranchRevert', false)) {
            		$command = 'git checkout ' . self::$startingBranch;
            		$result = $this->_runLocalCommand($command);

            	} else {
            		$command = 'git branch | grep \'*\' | cut -d\' \' -f 2';
            		$currentBranch = 'master';
            		$result = $this->_runLocalCommand($command, $currentBranch);

            		$scmData = $this->getConfig()->deployment('scm', false);

            		if ($result && is_array($scmData) && isset($scmData['branch']) && $scmData['branch'] != $currentBranch) {
        				$command = 'git branch | grep \'' . $scmData['branch'] . '\' | tr -s \' \' | sed \'s/^[ ]//g\'';
        				$isBranchTracked = '';
        				$result = $this->_runLocalCommand($command, $isBranchTracked);

        				if ($isBranchTracked == '') {
        					throw new Mage_Task_ErrorWithMessageException('The branch <purple>' . $scmData['branch'] . '</purple> must be tracked.');
        				}

        				$branch = $this->getParameter('branch', $scmData['branch']);
        				$command = 'git checkout ' . $branch;
        				$result = $this->_runLocalCommand($command);

        				self::$startingBranch = $currentBranch;
            		} else {
            			throw new Mage_Task_SkipException;
            		}
            	}
                break;

            default:
                throw new Mage_Task_SkipException;
                break;
        }


        $this->getConfig()->reload();

        return $result;
    }
}