settings.local.php

<?php
$database_suffix = '';

if (git_command_exists('git') && $git_describe = settings_execute_os_command('git rev-parse --abbrev-ref HEAD') ) {
  if (trim($git_describe) == 'HEAD') {
    $git_describe = settings_execute_os_command('git describe --all');
  }
  // Execute "git describe --all" and get the last part of heads/* as
  // the tag/branch.
  if (empty($git_describe)) {
    return;
  }
  $tag_branch_parts = explode('/', $git_describe);
  $release = end($tag_branch_parts);

  if (!empty($release)) {
    $database_suffix = '-' . $release;
  }
}

/**
 * Determines if a command exists on the current environment.
 *
 * @param string $command
 *   The command to check.
 *
 * @return bool
 *   TRUE if the command has been found; otherwise, FALSE.
 */
function git_command_exists($command) {
  $where_is_command = (PHP_OS == 'WINNT') ? 'where' : 'which';

  $command_return = settings_execute_os_command("$where_is_command $command");
  $output = !empty($command_return);
  return $output;
}

/**
 * Execute a system command and return the results.
 *
 * @param string $command
 *   The command to execute.
 *
 * @return string
 *   The results of the string execution.
 */
function settings_execute_os_command($command) {
  $process = proc_open(
    $command,
    array(
      // STDIN.
      0 => array("pipe", "r"),
      // STDOUT.
      1 => array("pipe", "w"),
      // STDERR.
      2 => array("pipe", "w"),
    ),
    $pipes
  );
  if ($process === FALSE) {
    return FALSE;
  }
  $stdout = stream_get_contents($pipes[1]);
  $stderr = stream_get_contents($pipes[2]);
  fclose($pipes[1]);
  fclose($pipes[2]);
  proc_close($process);

  return $stdout;
}

$databases = array (
  'default' =>
    array (
      'default' =>
    array (
      'database' => 'drupal'. str_replace('.', '-', trim($database_suffix)),
      'username' => 'drupal',
      'password' => 'drupal',
      'host' => 'localhost',
      'port' => '',
      'driver' => 'mysql',
      'prefix' => '',
    ),
    ),
);

// Reroute emails in dev mode.
$conf['reroute_email_enable'] = 1;

// Show all errors.
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);

// Turn off some performance caching.
$conf['preprocess_css'] = 0;
$conf['preprocess_js'] = 0;

$conf['less_devel'] = 1;
$conf['less_source_maps'] = 1;

// Replace the production GA account with the one we use for dev.
$conf['googleanalytics_account'] = 'UA-37674876-1';

// Set environment indicator.
$conf['environment_indicator_overwrite'] = TRUE;

$conf['environment_indicator_overwritten_name'] = 'LOCAL SERVER';
$conf['environment_indicator_overwritten_color'] = '#413D00';
$conf['environment_indicator_overwritten_text_color'] = '#BEBEBE';

adds a db suffix that matches the git branch name. So switching branches also switches databases. Awsome for use with drupal-vm and drush sql-create.

mostly taken from the environment module.