Externals Definitions

Sometimes it is useful to construct a working copy that is made out of a number of different checkouts. For example, you may want different subdirectories to come from different locations in a repository, or perhaps from different repositories altogether. You could certainly setup such a scenario by hand—using svn checkout to create the sort of nested working copy structure you are trying to achieve. But if this layout is important for everyone who uses your repository, every other user will need to perform the same checkout operations that you did.

Fortunately, Subversion provides support for externals definitions. An externals definition is a mapping of a local directory to the URL—and possibly a particular revision—of a versioned resource. In Subversion, you declare externals definitions in groups using the svn:externals property. You can create or modify this property using svn propset or svn propedit (see the section called “Why Properties?”). It can be set on any versioned directory, and its value is a multi-line table of subdirectories (relative to the versioned directory on which the property is set) and fully qualified, absolute Subversion repository URLs.

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$ svn propget svn:externals calc
third-party/sounds             http://sounds.red-bean.com/repos
third-party/skins              http://skins.red-bean.com/repositories/skinproj
third-party/skins/toolkit -r21 http://svn.red-bean.com/repos/skin-maker

he convenience of the svn:externals property is that once it is set on a versioned directory, everyone who checks out a working copy with that directory also gets the benefit of the externals definition. In other words, once one person has made the effort to define those nested working copy checkouts, no one else has to bother—Subversion will, upon checkout of the original working copy, also checkout the external working copies.

Note the previous externals definition example. When someone checks out a working copy of the calc directory, Subversion also continues to checkout the items found in its externals definition.

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$ svn checkout http://svn.example.com/repos/calc
A  calc
A  calc/Makefile
A  calc/integer.c
A  calc/button.c
Checked out revision 148.

Fetching external item into calc/third-party/sounds
A  calc/third-party/sounds/ding.ogg
A  calc/third-party/sounds/dong.ogg
A  calc/third-party/sounds/clang.ogg
…
A  calc/third-party/sounds/bang.ogg
A  calc/third-party/sounds/twang.ogg
Checked out revision 14.

Fetching external item into calc/third-party/skins
…

If you need to change the externals definition, you can do so using the regular property modification subcommands. When you commit a change to the svn:externals property, Subversion will synchronize the checked-out items against the changed externals definition when you next run svn update. The same thing will happen when others update their working copies and receive your changes to the externals definition.

The svn status command also recognizes externals definitions, displaying a status code of X for the disjoint subdirectories into which externals are checked out, and then recursing into those subdirectories to display the status of the external items themselves.

The support that exists for externals definitions in Subversion today can be a little misleading, though. First, an externals definition can only point to directories, not files. Second, the externals definition cannot point to relative paths (paths like ../../skins/myskin). Third, the working copies created via the externals definition support are still disconnected from the primary working copy (on whose versioned directories the svn:externals property was actually set). And Subversion still only truly operates on non-disjoint working copies. So, for example, if you want to commit changes that you’ve made in one or more of those external working copies, you must run svn commit explicitly on those working copies—committing on the primary working copy will not recurse into any external ones.

Also, since the definitions themselves use absolute URLs, moving or copying a directory to which they are attached will not affect what gets checked out as an external (though the relative local target subdirectory will, of course, move with renamed directory). This can be confusing—even frustrating—in certain situations. For example, if you use externals definitions on a directory in your /trunk development line which point to other areas of that same line, and then you use svn copy to branch that line to some new location /branches/my-branch, the externals definitions on items in your new branch will still refer to versioned resources in /trunk. Also, be aware that if you need to re-parent your working copy (using svn switch –relocate), externals definitions will not also be re-parented.

delete

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svn propdel -R svn:externals

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svn propdel PROPNAME

1、从第3000行开始，显示1000行。即显示3000~3999行

cat filename | tail -n +3000 | head -n 1000

2、显示1000行到3000行

cat filename| head -n 3000 | tail -n +1000

*注意两种方法的顺序

分解：
tail -n 1000：显示最后1000行
tail -n +1000：从1000行开始显示，显示1000行以后的
head -n 1000：显示前面1000行

3、用sed命令

sed -n '5,10p' filename

这样你就可以只查看文件的第5行到第10行。

1. Symptoms

While using Docker a user is unable to perform tasks such as pull new image or search for new images while the following error message appears:

# docker pull debian:8
Pulling repository debian
FATA[0053] Get https://index.docker.io/v1/repositories/library/debian/images: dial tcp: lookup index.docker.io: no such host

2. Solution

While this is a randomly occurring error it is frequently linked to a DNS resolution query by docker services. First, make sure you are running up to date docker installation. If this does not resolve your issue then try to resolve this error by restarting your docker service:

# service docker restart
Redirecting to /bin/systemctl restart  docker.service

In case that you are unable to restart your docker service at a present time you my try to temporarily resolve this issue by including the IP address of the host in question eg. index.docker.io to your /etc/hosts file. Resolve the IP address:

# dig index.docker.io +noall +answer +nocomments

; <<>> DiG 9.9.4-P2-RedHat-9.9.4-18.P2.fc20 <<>> index.docker.io +noall +answer +nocomments
;; global options: +cmd
index.docker.io.        30      IN      A       162.242.195.84

Next, include the IP address to your system’s /etc/hosts file:

# echo '162.242.195.84 index.docker.io' >> /etc/hosts

If you’ve found this entry, you probably ran into your first SVN Tree conflict. This is also called an ‘evil twin conflict’ in some other revision control systems.

The message generated by svn merge or later svn stat operations will look something like this:

A     C web-app/images/widget.png
      >   local obstruction, incoming add upon merge
...
Summary of conflicts:
  Tree conflicts: 1

The Cause

This special conflict message is created when the same file has been added to both the place your merging from as well as the place your merging to since the last merge. Since these evil twins both have completely different histories and no common state (as would exist if the image had been added before you branched), svn is totally unable to provide you advice. This is why you will see no `merge-left` or `merge-right` files.

The Solution

In the example above the same binary file has been added to both a branch and a trunk. Since the image is identical, the solution was simply to pick one. I picked the working copy.

    svn resolve --accept working ./web-app/images/widget.png


Another possible case is that two totally different files have been checked in with the same name and path. In this case, you’re going to need to rename one version and refactor the rest of your code to accommodate that name change. SVN has no easy way to do this so you’ll need to do it manually.

The last case is that the same file has been created but you need a super set of the functionality provided by both versions. Again, SVN does not offer any speedy tools for this so you’ll simply need to do a manual merger.

一次修复所有的错误信息

svn st | awk '{if ( $1 == "C") { print $2}}' | xargs svn resolve --accept working

cd \
du -h --max-depth=1|grep G|sort -n

找到最大的那个目录后进入该目录

再运行
du -h –max-depth=1|grep G|-n

如果没有结果可以运行
du -h –max-depth=1|grep M|sort -n

找出来以后看是否有用的文件

Git配置

git config --global user.name "robbin"   
git config --global user.email "fankai@gmail.com"
git config --global color.ui true
git config --global alias.co checkout
git config --global alias.ci commit
git config --global alias.st status
git config --global alias.br branch
git config --global core.editor "mate -w"    # 设置Editor使用textmate
git config -l  # 列举所有配置

用户的git配置文件~/.gitconfig

Git常用命令

查看、添加、提交、删除、找回，重置修改文件

git help <command>  # 显示command的help
git show            # 显示某次提交的内容
git show $id

git co  -- <file>   # 抛弃工作区修改
git co  .           # 抛弃工作区修改

git add <file>      # 将工作文件修改提交到本地暂存区
git add .           # 将所有修改过的工作文件提交暂存区

git rm <file>       # 从版本库中删除文件
git rm <file> --cached  # 从版本库中删除文件，但不删除文件

git reset <file>    # 从暂存区恢复到工作文件
git reset -- .      # 从暂存区恢复到工作文件
git reset --hard    # 恢复最近一次提交过的状态，即放弃上次提交后的所有本次修改

git ci <file>
git ci .
git ci -a           # 将git add, git rm和git ci等操作都合并在一起做
git ci -am "some comments"
git ci --amend      # 修改最后一次提交记录

git revert <$id>    # 恢复某次提交的状态，恢复动作本身也创建了一次提交对象
git revert HEAD     # 恢复最后一次提交的状态

查看文件diff

git diff <file>     # 比较当前文件和暂存区文件差异
git diff
git diff <$id1> <$id2>   # 比较两次提交之间的差异
git diff <branch1>..<branch2> # 在两个分支之间比较
git diff --staged   # 比较暂存区和版本库差异
git diff --cached   # 比较暂存区和版本库差异
git diff --stat     # 仅仅比较统计信息

查看提交记录

git log
git log <file>      # 查看该文件每次提交记录
git log -p <file>   # 查看每次详细修改内容的diff
git log -p -2       # 查看最近两次详细修改内容的diff
git log --stat      # 查看提交统计信息

tig

Mac上可以使用tig代替diff和log， `brew install tig`

Git 本地分支管理

查看、切换、创建和删除分支

git br -r           # 查看远程分支
git br <new_branch> # 创建新的分支
git br -v           # 查看各个分支最后提交信息
git br --merged     # 查看已经被合并到当前分支的分支
git br --no-merged  # 查看尚未被合并到当前分支的分支

git co <branch>     # 切换到某个分支
git co -b <new_branch> # 创建新的分支，并且切换过去
git co -b <new_branch> <branch>  # 基于branch创建新的new_branch

git co $id          # 把某次历史提交记录checkout出来，但无分支信息，切换到其他分支会自动删除
git co $id -b <new_branch>  # 把某次历史提交记录checkout出来，创建成一个分支

git br -d <branch>  # 删除某个分支
git br -D <branch>  # 强制删除某个分支 (未被合并的分支被删除的时候需要强制)

分支合并和rebase

git merge <branch>               # 将branch分支合并到当前分支
git merge origin/master --no-ff  # 不要Fast-Foward合并，这样可以生成merge提交

git rebase master <branch>       # 将master rebase到branch，相当于：
git co <branch> &amp;&amp; git rebase master &amp;&amp; git co master &amp;&amp; git merge <branch>

Git补丁管理(方便在多台机器上开发同步时用)

git merge <branch>               # 将branch分支合并到当前分支
git merge origin/master --no-ff  # 不要Fast-Foward合并，这样可以生成merge提交

git rebase master <branch>       # 将master rebase到branch，相当于：
git co <branch> &amp;&amp; git rebase master &amp;&amp; git co master &amp;&amp; git merge <branch>

Git补丁管理(方便在多台机器上开发同步时用)

git diff > ../sync.patch         # 生成补丁
git apply ../sync.patch          # 打补丁
git apply --check ../sync.patch  # 测试补丁能否成功

Git暂存管理

git stash                        # 暂存
git stash list                   # 列所有stash
git stash apply                  # 恢复暂存的内容
git stash drop                   # 删除暂存区

Git远程分支管理

git pull                         # 抓取远程仓库所有分支更新并合并到本地
git pull --no-ff                 # 抓取远程仓库所有分支更新并合并到本地，不要快进合并
git fetch origin                 # 抓取远程仓库更新
git merge origin/master          # 将远程主分支合并到本地当前分支
git co --track origin/branch     # 跟踪某个远程分支创建相应的本地分支
git co -b <local_branch> origin/<remote_branch>  # 基于远程分支创建本地分支，功能同上

git push                         # push所有分支
git push origin master           # 将本地主分支推到远程主分支
git push -u origin master        # 将本地主分支推到远程(如无远程主分支则创建，用于初始化远程仓库)
git push origin <local_branch>   # 创建远程分支， origin是远程仓库名
git push origin <local_branch>:<remote_branch>  # 创建远程分支
git push origin :<remote_branch>  #先删除本地分支(git br -d <branch>)，然后再push删除远程分支

Git远程仓库管理

git remote -v                    # 查看远程服务器地址和仓库名称
git remote show origin           # 查看远程服务器仓库状态
git remote add origin git@github:robbin/robbin_site.git         # 添加远程仓库地址
git remote set-url origin git@github.com:robbin/robbin_site.git # 设置远程仓库地址(用于修改远程仓库地址)
git remote rm <repository>       # 删除远程仓库

创建远程仓库

git clone --bare robbin_site robbin_site.git  # 用带版本的项目创建纯版本仓库
scp -r my_project.git git@git.csdn.net:~      # 将纯仓库上传到服务器上

mkdir robbin_site.git && cd robbin_site.git && git --bare init # 在服务器创建纯仓库
git remote add origin git@github.com:robbin/robbin_site.git    # 设置远程仓库地址
git push -u origin master                                      # 客户端首次提交
git push -u origin develop  # 首次将本地develop分支提交到远程develop分支，并且track

git remote set-head origin master   # 设置远程仓库的HEAD指向master分支

也可以命令设置跟踪远程库和本地库

git branch --set-upstream master origin/master
git branch --set-upstream develop origin/develop

In Cisco routers, the codes for a traceroute command reply are:

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! -- success
* -- time out
N -- network unreachable
H -- host unreachable
P -- protocol unreachable
A -- admin denied
Q -- source quench received (congestion)
? -- unknown (any other ICMP message)

作者: Laruence( )
本文地址: http://www.laruence.com/2011/06/23/2057.html
转载请注明出处

其实一直想写这个系列, 但是一想到这个话题的宽泛性, 我就有点感觉无法组织.

今天我也不打算全部讲如何调试一个PHP的Core文件, 也不会介绍什么是Coredump, 选择一个相对比较简单的方向来介绍, 那就是如何从PHP的Core文件中获取一些对我们重演这个Core有帮助的信息.

在这个过程中, 会涉及到对PHP的函数调用, PHP的传参, PHP的一些全局变量的知识, 这些知识在我之前的文章中都有过涉及, 大家可以翻阅: 深入理解PHP原理之函数 深入理解PHP原理之变量作用域等等.

首先, 让我们生成一个供我们举例子的Core文件:

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<?php
function recurse($num) {
      recurse(++$num);
}

recurse(0);

运行这个PHP文件:

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$ php test.php
Segmentation fault (core dumped)

这个PHP因为无线递归, 会导致爆栈, 从而造成 segment fault而在PHP的当前工作目录产生Coredump文件(如果你的系统没有产生Coredump文件, 那请查询ulimit的相关设置).

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$ ulimit -c unlimited
$ php test.php

好, 现在, 让我们删除掉这个test.php, 忘掉上面的代码, 我们现在仅有的是这个Core文件, 任务是, 找出这个Core产生的原因, 以及发生时候的状态.

首先, 让我们用gdb打开这个core文件:

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$ gdb php -c core.31656

会看到很多的信息, 首先让我们注意这段:

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Core was generated by `php test.php'.
Program terminated with signal 11, Segmentation fault.

他告诉我们Core发生的原因:”Segmentation fault”.

一般来说, 这种Core是最常见的, 解引用空指针, double free, 以及爆栈等等, 都会触发SIGSEGV, 继而默认的产生Coredump.

现在让我们看看Core发生时刻的堆栈:

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#0  execute (op_array=0xdc9a70) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:53
53          memset(EX(CVs), 0, sizeof(zval**) * op_array->last_var);
(gdb) bt
#0  execute (op_array=0xdc9a70) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:53
#1  0x00000000006ea263 in zend_do_fcall_common_helper_SPEC (execute_data=0x7fbf400210) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:234
#2  0x00000000006e9f61 in execute (op_array=0xdc9a70) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:92
#3  0x00000000006ea263 in zend_do_fcall_common_helper_SPEC (execute_data=0x7fbf400440) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:234
#4  0x00000000006e9f61 in execute (op_array=0xdc9a70) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:92
#5  0x00000000006ea263 in zend_do_fcall_common_helper_SPEC (execute_data=0x7fbf400670) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:234
.....

不停的按回车, 可以看到堆栈很深, 不停的是zend_do_fcall_common_helper_SPEC和execute的重复, 那么这基本就能断定是因为产生了无穷大的递归(不能一定说是无穷递归, 比如我之前文章中介绍深悉正则(pcre)最大回溯/递归限制). 从而造成爆栈产生的Core.

Ok, 那么现在让我们看看, Core发生在PHP的什么函数中, 在PHP中, 对于FCALL_* Opcode的handler来说, execute_data代表了当前函数调用的一个State, 这个State中包含了信息:

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(gdb)f 1
#1  0x00000000006ea263 in zend_do_fcall_common_helper_SPEC (execute_data=0x7fbf400210) at /home/laruence/package/php-5.2.14/Zend/zend_vm_execute.h:234
234               zend_execute(EG(active_op_array) TSRMLS_CC);
(gdb) p execute_data->function_state.function->common->function_name
$3 = 0x2a95b65a78 "recurse"
(gdb) p execute_data->function_state.function->op_array->filename
$4 = 0x2a95b632a0 "/home/laruence/test.php"
(gdb) p execute_data->function_state.function->op_array->line_start
$5 = 2

现在我们得到, 在调用的PHP函数是recurse, 这个函数定义在/home/laruence/test.php的第二行

经过重复验证几个frame, 我们可以看出, 一直是在重复调用这个PHP函数.

要注意的是, 为了介绍查看执行信息的原理, 我才采用原生的gdb的print来查看, 其实我们还可以使用PHP源代码中提供的.gdbinit(gdb命令编写脚本), 来简单的获取到上面的信息:

(gdb) source /home/laruence/package/php-5.2.14/.gdbinit
(gdb) zbacktrace
[0xbf400210] recurse() /home/laruence/test.php:3
[0xbf400440] recurse() /home/laruence/test.php:3
[0xbf400670] recurse() /home/laruence/test.php:3
[0xbf4008a0] recurse() /home/laruence/test.php:3
[0xbf400ad0] recurse() /home/laruence/test.php:3
[0xbf400d00] recurse() /home/laruence/test.php:3
[0xbf400f30] recurse() /home/laruence/test.php:3
[0xbf401160] recurse() /home/laruence/test.php:3
.....

关于.gdbinit, 是一段小小的脚本文件, 定义了一些方便我们去调试PHP的Core, 大家也可以用文本编辑器打开, 看看里面定义的一些快捷的命令, 一般来说, 我常用的有:

zbacktrace
print_ht**系列
zmemcheck

OK, 回归正题, 我们现在知道, 问题发生在/home/laruence/test.php的recurse函数的递归调用上了.

现在, 让我们来看看, 在调用这个函数的时候的参数是什么?

PHP的参数传递是依靠一个全局Stack来完成的, 也就是EG(argument_stack), EG在非多线程情况下就是executor_globals, 它保持了很多执行状态. 而argument_statck就是参数的传递栈, 保存着对应PHP函数调用层数相当的调用参数.

要注意的是, 这个PHP函数调用堆栈(层数)不和gdb所看到的backtrace简单的一一对应, 所以参数也不能直接和gdb的backtrace对应起来, 需要单独分析:

//先看看, 最后一次函数调用的参数数目是多少
(gdb) p (int )*(executor_globals->argument_stack->top_element - 2)
$13 = 1

//再看看, 最后一次函数调用的参数是什么
(gdb)  p **(zval **)(executor_globals->argument_stack->top_element - 3)
$2 = {value = {lval = 22445, dval = 1.1089303420906779e-319, str = {val = 0x57ad <Address 0x57ad out of bounds>, len = 7}, ht = 0x57ad, obj = {handle = 22445, handlers = 0x7}},
  refcount = 2, type = 1 '\001', is_ref = 0 '\0'}

好, 我们现在得到, 最后一次调用的参数是一个整数, 数值是22445

到了这一步, 我们就得到了这个Core发生的时刻的PHP层面的相关信息, 接下来, 就可以交给对应的PHP开发工程师来排查, 这个参数下, 可能造成的无穷大递归的原因, 从而修复这个问题..

后记: 调试PHP的Core是一个需要丰富经验的过程, 也许我今天介绍的这个例子太简单, 但是只要经常去挑战, 在遇到不懂的相关的知识的时候, 勇于去追根究底, 我相信大家终都可以成PHP Core杀手..

正则表达式，一个十分古老而又强大的文本处理工具，仅仅用一段非常简短的表达式语句，便能够快速实现一个非常复杂的业务逻辑。熟练地掌握正则表达式的话，能够使你的开发效率得到极大的提升。

正则表达式经常被用于字段或任意字符串的校验，如下面这段校验基本日期格式的JavaScript代码：

var reg = /^(\\d{1,4})(-|\\/)(\\d{1,2})\\2(\\d{1,2})$/; 
var r = fieldValue.match(reg);             
if(r==null)alert('Date format error!');


下面是技匠整理的，在前端开发中经常使用到的20个正则表达式。

• 1、校验密码强度 密码的强度必须是包含大小写字母和数字的组合，不能使用特殊字符，长度在8-10之间。

  ^(?=.\d)(?=.[a-z])(?=.*[A-Z]).{8,10}$

• 2、校验中文 字符串仅能是中文。

  ^[\u4e00-\u9fa5]{0,}$

• 3、由数字、26个英文字母或下划线组成的字符串

  ^\w+$

• 4、校验E-Mail 地址 同密码一样，下面是E-mail地址合规性的正则检查语句。

  [\w!#$%&’+/=?^_`{|}~-]+(?:\.[\w!#$%&’+/=?^_`{|}~-]+)@(?:[\w](?:[\w-][\w])?\.)+\w?

• 5、校验身份证号码

  下面是身份证号码的正则校验。15 或 18位。

  15位：

  ^[1-9]\d{7}((0\d)|(1[0-2]))(([0|1|2]\d)|3[0-1])\d{3}$

18位：

^[1-9]\\d{5}[1-9]\\d{3}((0\\d)|(1[0-2]))(([0|1|2]\\d)|3[0-1])\\d{3}([0-9]|X)$

• 6、校验日期 “yyyy-mm-dd“ 格式的日期校验，已考虑平闰年。

  ^(?:(?!0000)[0-9]{4}-(?:(?:0[1-9]|1[0-2])-(?:0[1-9]|1[0-9]|2[0-8])|(?:0[13-9]|1[0-2])-(?:29|30)|(?:0[13578]|1[02])-31)|(?:[0-9]{2}(?:0[48]|[2468][048]|[13579][26])|(?:0[48]|[2468][048]|[13579][26])00)-02-29)$

• 7、校验金额 金额校验，精确到2位小数。

  ^[0-9]+(.[0-9]{2})?$

• 8、校验手机号 下面是国内 13、15、18开头的手机号正则表达式。

  ^(13[0-9]|14[5|7]|15[0|1|2|3|5|6|7|8|9]|18[0|1|2|3|5|6|7|8|9])\d{8}$

• 9、判断IE的版本 IE目前还没被完全取代，很多页面还是需要做版本兼容，下面是IE版本检查的表达式。

  ^.MSIE 5-8?(?!.*Trident\/[5-9]\.0).$

• 10、校验IP-v4地址 IP4 正则语句。

  \b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

• 11、校验IP-v6地址 IP6 正则语句。

  (([0-9a-fA-F]{1,4}:){7,7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|fe80:(:[0-9a-fA-F]{0,4}){0,4}%[0-9a-zA-Z]{1,}|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]))

• 12、检查URL的前缀 应用开发中很多时候需要区分请求是HTTPS还是HTTP，通过下面的表达式可以取出一个url的前缀然后再逻辑判断。

  if (!s.match(/^[a-zA-Z]+:\/\//))
  {

  s = 'http://' + s;

  }

• 13、提取URL链接 下面的这个表达式可以筛选出一段文本中的URL。
  ^(f|ht){1}(tp|tps):\/\/([\w-]+\.)+[\w-]+(\/[\w- ./?%&=]*)?

• 14、文件路径及扩展名校验 验证文件路径和扩展名

  ^([a-zA-Z]\:|\\)\\([^\\]+\\)[^\/:?”<>|]+\.txt(l)?$

• 15、提取Color Hex Codes 有时需要抽取网页中的颜色代码，可以使用下面的表达式。

  \\#([a-fA-F]|[0-9]){3,6}

• 16、提取网页图片 假若你想提取网页中所有图片信息，可以利用下面的表达式。

  \\< *[img][^\\>]*[src] *= *[\\"\\']{0,1}([^\\"\\'\\ >]*)

• 17、提取页面超链接 提取html中的超链接。

  (<a\\s*(?!.*\\brel=)[^>]*)(href="https?://)((?!(?:(?:www\\.)?'.implode('|(?:www\\.)?', $follow_list).'))[^"]+)"((?!.*\\brel=)[^>]*)(?:[^>]*)>

• 18、精炼CSS 通过下面的表达式，可以搜索相同属性值的CSS，从而达到精炼代码的目的。

  ^\\s*[a-zA-Z\\-]+\\s*[:]{1}\\s[a-zA-Z0-9\\s.#]+[;]{1}

• 19、抽取注释 如果你需要移除HMTL中的注释，可以使用如下的表达式。

• 20、匹配HTML标签 通过下面的表达式可以匹配出HTML中的标签。

  </?\w+((\s+\w+(\s=\s(?:”.?”|’.?’|[\^’”>\s]+))?)+\s|\s)/?>

正则表达式的相关语法

下面是我找到的一张非常不错的正则表达式 Cheat Sheet，可以用来快速查找相关语法。 

学习正则表达式

我在网上看到了一篇相当不错的正则表达式快速学习指南，有兴趣继续深入学习的同学可以参考。

正则表达式在线测试工具

regex101是一个非常不错的正则表达式在线测试工具，你可以直接在线测试你的正则表达式哦。

ll -Sh *.mp4 | grep ^[^d] | awk '{print $5,$9;}'