啟動 Mac OS X 的 OpenLDAP

三部曲
1. slappasswd 建立新的 rootpw
2. 編輯 /etc/openldap/slapd.conf 內的 suffix, rootdn, rootpw
3. slapd -d 255
Reference:
starting OpenLDAP on Mac OS X

LWP Chunked Way

在讀取 || 傳送大量資料的時候，可以利用 IO::* 這類模組去一次讀取其中一段資料 (Chunk) 就寫入暫存檔 || 送出，來避免對記憶體造成負擔的手法可說相當常用。也是 HTTP Server 用來做 Streaming 或是 Long Polling / Comet 的基礎。

Client 端的用法就沒有那麼絢麗的名字了（開發 Client 的人沒有必要用絢麗的名字震懾老闆？:p）。LWP 對 Chunk 手法也有支援，不過在 GET 和 POST 兩種 HTTP 動做的支援方式分別使用了接受 callback 和利用全域變數啟用的方式，有點不一致，特此紀錄一筆。

GET 使用 Chunk 的方式在 lwpcook 有詳盡記載。在 LWP::UserAgent 物件呼叫 request 方法時多傳入一個 callback 即可。

POST 動作其實也應該可以提供 callback。想像起來應該是這樣：

大概是反正多數時候只能寫 $socket->write($chunk)，所以乾脆就給個全域變數當作開關？

$HTTP::Request::Common::DYNAMIC_FILE_UPLOAD = 1;

雖然有 callback 的話應該還是有點用途的。

class variables in Moose

Moose attribute didn't allow the reference rather than a CODE reference as a default value. That prevents the objects shared a attribute when initializing. Actually this is a good design. But How should I do when needing a shared attribute between objects? I may refer this as the concept of class variable.

The state variable in CODE reference may be competent with this role.

A Counter as an example here. We define a Counter class here.



A counter has a attribute "value" and a method "inc" to increment it.

Then We define a Person class.



The Person class has a attribute "name" and a shared attribute "count". The Counter is a state variable return from a anonymous CODE reference. That's the trick.

The BUILD hook increment the counter everytime a new Person is constructed.

Then we examinate the shared variable.



A global variable in package name may still work. But this way uses 'has' syntax sugar. :p

If you use builder to replace the default option. the subroutine used by the builder is just the class variable accessor from Class name, returning value as $person->count().

Mysterious Timestamp

時間轉換大概是最惱人的「小」問題之一，每個語言的標準處理方式不盡相同。Perl 的 localtime() 是月份從 0 開始到 11 結束，Ruby 的 DateTime 是月份是從 1 開始的，不過 Perl 的 DateTime 月份也從 1 開始 (LOL)。背誦這些東西大概會發瘋。

不過 Epoch 沒有這個問題，任何語言上的 Epoch 應該都是一致的，有的只是時差問題，使用 Epoch 來初始時間物件大概是避開這問題的好方法之一，特別在不同語言間交換時間資料時，用 Epoch 交換後怎麼 format 都不會出問題。所以有些時間模組大概會像 Perl 的 DateTime 一樣實作 from_epoch() 這種 constructor。

就這點設計而言，Badger::Timestamp 大概是最好用的時間模組，其 constructor 支援 DateTime 模組的方式初始化外，還可以餵食 Epoch 和 ISO 格式的時間字串。一個簡單的 Epoch/ISO converter 只要八行。

什麼，你問說這八行程式有什麼用，有些跑了好幾年的 unix 系統上有著 crontab 執行著需要 timestamp 來分辨執行區段的分析器，有些要當天的零分零秒，有些要隔天的零分零秒。壞掉時有人會要你一定要「人工」處理，這八行就就是這樣來的。

附帶一提， Javascript 的 Date.UTC 和 Perl 的 localtime() 一樣，都是月份從 0 開始。

為什麼Javascript的月份是從0開始的 (-_-) w3schools.com/jsref/jsref_ut…

— Alec Chen (@alec929) February 28, 2012

和 Badger::Timestamp 很像的 moment.js這時候就很好用了，其 constructor 用陣列初始化時雖然還是沒有改用 1 作為月份起始著實也讓我驚訝了一下。好險，這 constructor 支援用 Epoch 初始化(不過承襲 javascript 的慣例，是 millisecond)，還可以用 Date.parse() 支援的字串初始化。這兩招可以避開月份的問題。

meet git-p4

For some reasons, in recent works I have to use Perforce, the revision control system used by Perl core team before 2008. Unfortunately, perforce lacks of distributed features and leads to heavy branching. In this developing, these two problems often interrupted programmers with conflicts hardly to solve. Bad workflow design also makes members forget to check out before editing randomly. A git subcommand git-p4 lets you use the great tool git locally with the smooth integration to perforce server.

The steps to configure on kernel.org are currently unavailable. The official site of Perforce saved a copy. Following normal steps to write .p4config to setup p4client and install p4 and git-p4 into $PATH, $ git p4 clone //depos/path /local/path would just work. After local commit of git, $ git p4 rebase && git p4 submit works just like $ git pull --rebase && git push to remote git repository.

By the way, if you use Mercurial there is also a perforce extension can enable hg to clone perforce repository directly with a few of setup.

However, I strongly recommend perforce users migrating to modern distributed revision control system. After all, all the best companies and organizations have given Git / Mercurial a big hug, such as Github, BitBucket, Apple, Google Code, Perl, Rails, Gnome, Debian, Android and Linux Kernel. The git-p4 is a good transformer.

2012-04-26 update:
The git-p4 is now part of the git distribution and the version on github is no longer updated and doesn't work.

Arrange bashrc

A simple recursive function can have aid on arranging bashrc files in a clear structure.



Add a line to source it in ~/.bashrc first, and then collect similar rc files into directories respectively.

If a bunch of bash completions were put inside ~/.bash_completion/, like

~/.bash_completion
|-- hg
|-- git
|   |-- git
|   |-- gitk
|   `-- git-common
`-- svk

just one more line

  load $HOME/.bash_completion

would load whole completions.

You may also have many aliases, environment variables, function definitions for different OS like this

~/.bashrc.d
|-- linux
|   |-- aliases
|   |-- env
|   `-- functions
|-- freebsd
|   |-- aliases
|   |-- env
|   `-- functions
`-- darwin
    |-- aliases
    |-- env
    `-- functions

Just one another line

  load "$HOME/.bashrc.d/$(lower $(uname))"

can load correct system-specified rc files.

MySQL 5.5.10 homebrew install issue

Coming after the mysql 5.1.52 homebrew install issue, the just released mysql 5.5.10, which solved the previous problem, has another issue.

When starting mysql daemon with mysql.server script, it showed error message like

ERROR! The server quit without updating PID file (/usr/local/var/mysql/data/*********.pid).

The new homebrew instruction to install mysql makes its default $datadir to be $basedir/data but the setting of $datadir in mysql.server line 70 didn't be fixed to corresponded to the change.

Adjust $datadir in script or just use boot parameter --data-dir=/usr/local/Cellar/mysql/5.5.10/data/ makes mysql.server work.

Tasting Perl6

At the moment that the first release of Rakudo Star has been announced over four months, binary packages or tested build in package managers have been provided in varieties of OS. If we want to taste Perl6 on Mac OS X, the best choice seems to be using Homebrew. Just type in $ brew install rakudo-star and run $ perl6. Rakudo Star in Homebrew has been updated to the newest version: 2010.10.

On Debian-like system, the best one should be using PPA of dexter on LaunchPad. The version falls behind Homebrew a little to be 2010.09. Because the Rakudo Star requires Parrot 2.8+, we also have to add PPA of Parrot to satisfy. Command $ sudo apt-add-repository ppa:dexter/rakudo-pkg ppa:dexter/parrot-pkg and run update, install. Then have fun!

Intro to App::CLI

My first meet with App::CLI is in the summer of 2008, trying to write JiftyX::Fixtures. Without abundant PODs coming with this module, it took me almost one day to understand this module through trial and error. Since, I write this intro to reveal more power from this module; even I have contribute some code and DOCs to the project.

Actually, App::CLI is a really powerful module having central idea similar to the dispatcher in many web application frameworks such as Rails. When we are trying to create yet another handy CLI tool for our daily working, here is a recommended architecture to use App::CLI:

MyApp                  
-> The kernel of our new tool

MyApp::*               
-> All other module forming the mechanism 
-> of our new tool, e.g. MyApp::Config
-> for loading configuration

MyApp::Command         
-> The dispatcher serving the invoking commands

MyApp::Command::*      
-> All subcommands invoked by MyApp::Command

MyApp::Command::*::*   
-> All subsubcommands invoked by specific subcommand

MyApp::Command::*::*::*
-> subsubsubcommands *god*

After deciding what command we need to implement, we only have two things should be done. The first is making MyApp::Command be able to dispatch. What we need to do is only add use base qw(App::CLI); into it.

Now, in MyApp.pm or our script, where we want to invoke command, we can just say

MyApp::Command->dispatch();

MyApp::Command would automatically use @ARGV to determine what (sub)command it should invoke and find its package to *require*. For example, if we type $ myapp list user --sort age in terminal, the @ARGV would be qw(list user --sort age), and MyApp::Command would require MyApp::Command::List::User, create its instance as $cmd, assign $cmd->{sort} as 'age', finally invoke $cmd->run_command().

So, The second thing, most of we need to effort, is to implement our (sub)commands. it's a bit like writing Controllers of Rails. If the URL matches /foo/bar/:id, the Action #list() of Controller Foo::Bar would handle the request, and @id would be assign value. If users type $ myapp list nickname --name /mark/ MyApp::Command::List::Nickname would handle the command and $instance->{name} would be assign string /mark/. For this case, we can write as below.

package MyApp::Command::List;
use base qw(App::CLI::Command);
use constant subcommands => qw(User Nickname);
use constant options => (
    "h|help" => "help",
);

sub run {
    my ($self, @args) = @_;
    if ($self->{help}){
        # output PODs when $ myapp list --help
    }
    # do something when user type like 
    # $ myapp list arg1 arg2 --opt1 --opt2 opt_arg2
    # and arg1 doesn't equal to User or Nickname
}



package MyApp::Command::List::Nickname;
use base qw(App::CLI::Command);
use constant options => (
    "name=s"  => "name",
);

sub run {
    my ($self, @args) = @_;
    $name = $self->{name} #=> /mark/
    # query the data base via condition /mark/
}

It completes. Note the we can specify all possible subcommands in constant subcommands of and give all possible options in constant options to all (sub)commands and just implement &run() the (sub)command would be done. And finally, note we can cascading subcommands infinitely. That is the core power of this module starting from v0.2.

Enjoy.

Keep favorite info pages in $HOME

Info is a handy document system most emacs fans love. We can learn Info, Emacs Basics, Emacs Lisp, Magit and blah blah blah through the system and look up any detail every time we need without leaving Emacs, so that I install many info pages into /usr/local/info, /usr/share/info and /usr/share/local/info. However, when I need to migrate all data to new computer, keeping my info pages is really a nightmare. So I add a few of lines shown below into ~/.emacs

(custom-set-variables
  '(Info-default-directory-list 
     (append Info-default-directory-list 
             '("~/.info"))))

and put all info pages I collected before into ~/.info

Now I just need to migrate all files in my $HOME to new computer.

Two ZSH conventions for switchers from BASH

When starting to learn UNIX, I enjoyed with the well-designed Debian 3.1 and the bash completions coming with it. At that time the ZSH on Debian wasn't well configured for a newbie having no direction in dark.

Actually, the ZSH was set as a handy tool on recent releases of Debian-like system. For a longtime user of BASH, the default setting of backward-kill-word is confusing: it never stop with DASH, UNDERSCORE, and SLASH, etc. However, it's easy to modify the action through manipulate the $WORDCHARS variable which including all chars treated as alphabet in ZSH. For example,

export WORDCHARS=${WOARCHARS:s/-//}

exclude the dash sign from $OWRDCHARS, or you can just export the $WORDCHARS you want.

The second is ZSH can only auto-completed from first choice to the final by default. Adding bindkey '^[[Z' reverse-menu-complete to ~/.zshrc makes me not being afraid of pressing tab too fast.

References:
[1] stackoverflow.com
[2] zsh mailing list

Fullscreen Emacs on Mac OS X from tarball

Emacs 23.2 in trunk doesn't support fullscreen on Mac OS X.

Japanese hacker typester do a patch for this.

Following is a quick step-by-step instruction to compile emacs 23.2 supporting fullscreen with this patch.

cd /tmp

wget http://ftp.twaren.net/Unix/GNU/gnu/emacs/emacs-23.2.tar.gz

wget http://github.com/downloads/typester/emacs/feature-fullscreen.patch

tar xzvf emacs-23.2.tar.gz

cd emacs-23.2

patch -p1 < /tmp/feature-fullscreen.patch

./configure --with-ns

make 

sudo make install

mv nextstep/Emacs.app ~/Applications

Reference:
[1] Emacs Wiki
[2] sanityinc.com
[3] Citizen428

practical python trick about static variables

It seems there is no syntax to declare static variables in Python. Fortunately, here is a useful trick to accomplish the goal.

sudo on OpenLDAP

sudo 官方文件 和 這篇 SOP (on Ubuntu) 算是寫得最實用的文件。

不過呢，還是很多廢話。

這兩篇文章的內容可以總結如下：

1. 準備好可以使用的 OpenLDAP 伺服器，這份文件 寫得比較詳盡。幫他加上 sudo.schema，並用 migration_sudo.pl 轉換並匯入 sudoers。

2. 裝好支援 LDAP 的 sudo。Debian-like System 是 sudo-ldap 這個套件。

3. /etc/nsswitch.conf 加上 sudoer: ldap

4. /etc/ldap/ldap.conf 或是 /etc/sudo-ldap.conf (在 Debian 是同一檔案) 加上 sudoers_base [SUDOers DN]

Fun Weekend

忙了一整個禮拜，今天又唸了一整天書，於是乎覺得需要休息一下，想起開學時就想去吃看看的鼎泰豐，到現在還不知道在哪，拎起夾克，挾住一本書在腋下就出發來去探探路。

在 GMap 的帶路下，很快就到了信義路上的鼎泰豐




飽餐一頓之後決定輕鬆地走路回宿舍。

沿著金山南路往南走，走過熟悉又陌生的台師大門口。大三時因為擔心研究所筆試臨場反應不好，要是沒考上就得去盡忠報國，所以特別提前一年報了台大光電的筆試來試刀。走過那年的考場，兩年裡準備考試的酸甜苦辣倒也反芻了一遍。

轉了個彎走進師大路，比對著記憶裡的街角，今晚的師大夜市一般的人潮洶湧。不一樣的是路邊的那個小廣場，今晚圍了一群人。湊上去一看，是個有趣的大叔，看起來快到不惑之年，一把小提琴流暢的拉著，一支音響丟在旁邊為他伴奏，不時還擺個花式娛樂大家一下。

老實說看到的時候還滿驚訝的，台北街頭藝人不是沒有，但是大多是吉他或是歌唱表演。小提琴的表演呢，雖說最初就是以類似這樣的表演形式出現在大家面前，我一直以為現在只有法國或是義大利的街頭才看得到這種光景。就像是講起街頭探戈，人們總是想起阿根廷一樣。

師大路小提琴表演一 from Shelling Ford on Vimeo.

我到的時候已經晚了，一曲拉畢，大叔準備回家休息，旁邊有人喊起安可，大叔竟然用台語說：我又不是你阿伯，隨便你叫安可喔，好拉，我就再拉一首比較輕柔一點的，讓各位有好心情，慢慢回家睡個好覺。*XD*

師大路小提琴表演二 from Shelling Ford on Vimeo.

拉完這首大家也就散了，大叔在打包的時候，帶著一個五歲小孩的媽上去問他說：你還會不會在這裡表演。小鬼頭看起來非常想學琴，大叔還跟他拉咧了一下：你長這麼帥，學琴一定很吃香拉。我也是在路上看人家表演就跟著去學了。能不能賺錢是一回事，自己學得很高興比較重要，不過爸媽可能就要拉緊褲帶了。XD

到台北讀書也半年，大部分時候看到的台北，總在不經意的時候留露一點張愛玲式的荒涼，或是白先勇式的寂寞吧。相較起來，台南或許是繁華落盡了，但是敦厚的中國式文化，卻是深植人心的，雖然不若台北資源豐富，但台南給人的感覺是個有氣質的都市，好比美女不需濃妝豔抹，儀態自華。

不過今晚的表演讓我看到不一樣風貌的台北，或許只是一小部份人，但是還有人願意追尋藝術和文化最根本的那種感動，拿著一把小提琴，在街頭和觀眾同樂。這讓人覺得台北或許還是值得居住的城市吧。

Common Abbreviation in LDAP

DC: Domain Country
OU: Organization Unit
CN: Common Name
DN: Distinguish Name
RDN: relative distinguish name
LDIF: LDAP Interchange Format
DIT: Directory Information Tree

FDTD tips

When using BPML, external wall should be treated as PECs for simplicity no matter how many the maximum sigma is. The best way to do that is setting initial field value on external wall to be zero, and then don't update field value of any point on the wall.

That is to say, it could be written as



Saving a few of computing resource.

 

Injecting one module into another in Python

Here is a simple code snippet to do that. Saving it to an individual file and import it in other module to use it.



Using exec statement is also good, but need to pass globals() or locals() dictionary to the function executing exec statement.

Doing dirty things in Python is really not easy...:/

 

Assign initial value to a pointer

Today I suddenly got an idea. Most of time when we use pointer, we create a variable, and assign initial value to it, and then take its address become the value of a new pointer for succeeding use. But we create a redundant identifier here.

In fact, we could always create a fundamental type pointer and assign initial value to it through dereference operator like this snippet.



and no redundant variable here.

But when we define a simple struct like this.



We should assign initial value through arrow operator like third and fourth line in below snippet. Using brace to assign value as the same as first snippet is wrong syntax.



With a complex struct definition, this way increases many redundant code. Using brace to assignment initial value without creating redundant identifier could be done like this.



But I consider writing (*aPtr) = { 1, 2 }; may be the most intuitive way and it doesn't conflict with other syntax in C.

 

Library for Numerical Computing

Briefly summarize some numerical library here. It looks there are too many useful tools. Either for parallel computing or for matrix, numerical calculating and plotting.

PLOT:

MatPlotLib: it seems to be the most awesome plotting tool among this list

PGPlot: C library, also have binding in Perl, Python,Ruby

PLPlot: cross-platform plot library, also have binding in Perl

Scientific Python

MRPlot


PARALLEL:

MPI Ruby: MPI Ruby binding

PyMPI: MPI integrated Python interpreter

MPI for Python Python MPI binding

Simple Remote Python : SrPy

Parallel Python


CALCULATION:

Perl Data Language: difficult to be categorized. Including calculating, plotting together. include FFTW, PGPlot, PLPlot, and many data processing tool such as HDF. Awesome Environment!

MPMath: Multi-Precision math functions collection.

RNUM

NArray

LibFFTW, also have binding in Perl, Ruby

Ruby DCL

LAPACK

SciPy

NumPy

GNU Scientific Library: C library, also have bindings in Ruby named Ruby/GSL and Ruby-GSL. and Python

RSRuby: bridge between Ruby and R

ARTICLES:

Ruby for Science