http://blog.csdn.net/feiniao1221/article/details/7516421
以gerrit-trigger-plugin为例，下面的链接都是从相应页面上直接拷贝的。

法一：不用github的账号，打开这个库在github上的主页，运行下面命令即可

read only
运行命令$git clone https://github.com/jenkinsci/gerrit-trigger-plugin.git

下面的三种方法都要先在github上注册账户，然后生成相应的ssh key，并把public key添加到个人账户里面，详见github帮助
read+write
$git clone git@github.com:flyingbird1221/gerrit-trigger-plugin.git 

read+write
$git clone https://flyingbird1221@github.com/flyingbird1221/gerrit-trigger-plugin.git  
会提示输入密码，注意此处的密码不是你在github上账户的密码，而是当前登录系统用户的密码。
read only
$git clone git://github.com/flyingbird1221/gerrit-trigger-plugin.git

http://www.cnblogs.com/yaoshan/archive/2013/01/10/2854281.html
git clone 命令参数：
usage: git clone [options] [–] <repo> [<dir>]

-v, –verbose         be more verbose
-q, –quiet           be more quiet
–progress            force progress reporting
-n, –no-checkout     don’t create a checkout
–bare                create a bare repository
–mirror              create a mirror repository (implies bare)
-l, –local           to clone from a local repository
–no-hardlinks        don’t use local hardlinks, always copy
-s, –shared          setup as shared repository
–recursive           initialize submodules in the clone
–recurse-submodules  initialize submodules in the clone
–template <template-directory>
directory from which templates will be used
–reference <repo>    reference repository
-o, –origin <name>   use <name> instead of ‘origin’ to track upstream
-b, –branch <branch>
checkout <branch> instead of the remote’s HEAD
-u, –upload-pack <path>
path to git-upload-pack on the remote
–depth <depth>       create a shallow clone of that depth
–separate-git-dir <gitdir>
separate git dir from working tree
-c, –config <key=value>
set config inside the new repository

参数挺多，但常用的就几个：

1. 最简单直接的命令
git clone xxx.git

2. 如果想clone到指定目录
git clone xxx.git “指定目录”

3. clone时创建新的分支替代默认Origin HEAD（master）
git clone -b [new_branch_name]  xxx.git

4. clone 远程分支
git clone 命令默认的只会建立master分支，如果你想clone指定的某一远程分支(如：dev)的话，可以如下：

A. 查看所有分支(包括隐藏的)  git branch -a 显示所有分支，如：

* master
remotes/origin/HEAD -> origin/master
remotes/origin/dev
remotes/origin/master
B.  在本地新建同名的(“dev”)分支，并切换到该分支

git checkout -t origin/dev 该命令等同于：
git checkout -b dev origin/dev