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  • What is the difference between "su --command" and "su --session-command"?

    - by oliver
    Running # su - oliver --command bash gives a shell but also prints the warning bash: no job control in this shell, and indeed Ctrl+Z and fg/bg don't work in that shell. Running # su - oliver --session-command bash gives a shell without printing the warning, and job control indeed works. The suggestion to use --session-command comes from Starting a shell from scripts using su results in "no job control in this shell" which states "[a security fix for su] changed the behavior of the -c option and disables job control inside the called shell". But I still don't quite understand this. When should one use --command and when should one use --session-command? Is --command (aka -c) more secure? Or should one always use --session-command, and --command is just left in for backwards compatibility? FWIW, I'm using RHEL 6.4.

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  • Design pattern for window management in a Java Swing app

    - by Lord Torgamus
    I've just started creating my very first little Java Swing app. When the program opens, it brings up a single, simple window with a label and a couple buttons. Clicking one of those buttons is supposed to wipe out the welcome screen and replace it with a totally different panel. I'm not sure what the best way to create that functionality is. One method would be to pass my JFrame as an argument into... just about every other component, but that feels hacky to me. Or, there's making each panel double as an action listener, but that doesn't seem right, either. Is there a design pattern I should be applying here? "Replace the contents of the main — and only — window" must be a reasonably common operation. A name for the pattern would be enough; I can use Google on my own from there. (I wouldn't say no to a longer explanation, though.)

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  • Understanding C# async / await (2) Awaitable / Awaiter Pattern

    - by Dixin
    What is awaitable Part 1 shows that any Task is awaitable. Actually there are other awaitable types. Here is an example: Task<int> task = new Task<int>(() => 0); int result = await task.ConfigureAwait(false); // Returns a ConfiguredTaskAwaitable<TResult>. The returned ConfiguredTaskAwaitable<TResult> struct is awaitable. And it is not Task at all: public struct ConfiguredTaskAwaitable<TResult> { private readonly ConfiguredTaskAwaiter m_configuredTaskAwaiter; internal ConfiguredTaskAwaitable(Task<TResult> task, bool continueOnCapturedContext) { this.m_configuredTaskAwaiter = new ConfiguredTaskAwaiter(task, continueOnCapturedContext); } public ConfiguredTaskAwaiter GetAwaiter() { return this.m_configuredTaskAwaiter; } } It has one GetAwaiter() method. Actually in part 1 we have seen that Task has GetAwaiter() method too: public class Task { public TaskAwaiter GetAwaiter() { return new TaskAwaiter(this); } } public class Task<TResult> : Task { public new TaskAwaiter<TResult> GetAwaiter() { return new TaskAwaiter<TResult>(this); } } Task.Yield() is a another example: await Task.Yield(); // Returns a YieldAwaitable. The returned YieldAwaitable is not Task either: public struct YieldAwaitable { public YieldAwaiter GetAwaiter() { return default(YieldAwaiter); } } Again, it just has one GetAwaiter() method. In this article, we will look at what is awaitable. The awaitable / awaiter pattern By observing different awaitable / awaiter types, we can tell that an object is awaitable if It has a GetAwaiter() method (instance method or extension method); Its GetAwaiter() method returns an awaiter. An object is an awaiter if: It implements INotifyCompletion or ICriticalNotifyCompletion interface; It has an IsCompleted, which has a getter and returns a Boolean; it has a GetResult() method, which returns void, or a result. This awaitable / awaiter pattern is very similar to the iteratable / iterator pattern. Here is the interface definitions of iteratable / iterator: public interface IEnumerable { IEnumerator GetEnumerator(); } public interface IEnumerator { object Current { get; } bool MoveNext(); void Reset(); } public interface IEnumerable<out T> : IEnumerable { IEnumerator<T> GetEnumerator(); } public interface IEnumerator<out T> : IDisposable, IEnumerator { T Current { get; } } In case you are not familiar with the out keyword, please find out the explanation in Understanding C# Covariance And Contravariance (2) Interfaces. The “missing” IAwaitable / IAwaiter interfaces Similar to IEnumerable and IEnumerator interfaces, awaitable / awaiter can be visualized by IAwaitable / IAwaiter interfaces too. This is the non-generic version: public interface IAwaitable { IAwaiter GetAwaiter(); } public interface IAwaiter : INotifyCompletion // or ICriticalNotifyCompletion { // INotifyCompletion has one method: void OnCompleted(Action continuation); // ICriticalNotifyCompletion implements INotifyCompletion, // also has this method: void UnsafeOnCompleted(Action continuation); bool IsCompleted { get; } void GetResult(); } Please notice GetResult() returns void here. Task.GetAwaiter() / TaskAwaiter.GetResult() is of such case. And this is the generic version: public interface IAwaitable<out TResult> { IAwaiter<TResult> GetAwaiter(); } public interface IAwaiter<out TResult> : INotifyCompletion // or ICriticalNotifyCompletion { bool IsCompleted { get; } TResult GetResult(); } Here the only difference is, GetResult() return a result. Task<TResult>.GetAwaiter() / TaskAwaiter<TResult>.GetResult() is of this case. Please notice .NET does not define these IAwaitable / IAwaiter interfaces at all. As an UI designer, I guess the reason is, IAwaitable interface will constraint GetAwaiter() to be instance method. Actually C# supports both GetAwaiter() instance method and GetAwaiter() extension method. Here I use these interfaces only for better visualizing what is awaitable / awaiter. Now, if looking at above ConfiguredTaskAwaitable / ConfiguredTaskAwaiter, YieldAwaitable / YieldAwaiter, Task / TaskAwaiter pairs again, they all “implicitly” implement these “missing” IAwaitable / IAwaiter interfaces. In the next part, we will see how to implement awaitable / awaiter. Await any function / action In C# await cannot be used with lambda. This code: int result = await (() => 0); will cause a compiler error: Cannot await 'lambda expression' This is easy to understand because this lambda expression (() => 0) may be a function or a expression tree. Obviously we mean function here, and we can tell compiler in this way: int result = await new Func<int>(() => 0); It causes an different error: Cannot await 'System.Func<int>' OK, now the compiler is complaining the type instead of syntax. With the understanding of the awaitable / awaiter pattern, Func<TResult> type can be easily made into awaitable. GetAwaiter() instance method, using IAwaitable / IAwaiter interfaces First, similar to above ConfiguredTaskAwaitable<TResult>, a FuncAwaitable<TResult> can be implemented to wrap Func<TResult>: internal struct FuncAwaitable<TResult> : IAwaitable<TResult> { private readonly Func<TResult> function; public FuncAwaitable(Func<TResult> function) { this.function = function; } public IAwaiter<TResult> GetAwaiter() { return new FuncAwaiter<TResult>(this.function); } } FuncAwaitable<TResult> wrapper is used to implement IAwaitable<TResult>, so it has one instance method, GetAwaiter(), which returns a IAwaiter<TResult>, which wraps that Func<TResult> too. FuncAwaiter<TResult> is used to implement IAwaiter<TResult>: public struct FuncAwaiter<TResult> : IAwaiter<TResult> { private readonly Task<TResult> task; public FuncAwaiter(Func<TResult> function) { this.task = new Task<TResult>(function); this.task.Start(); } bool IAwaiter<TResult>.IsCompleted { get { return this.task.IsCompleted; } } TResult IAwaiter<TResult>.GetResult() { return this.task.Result; } void INotifyCompletion.OnCompleted(Action continuation) { new Task(continuation).Start(); } } Now a function can be awaited in this way: int result = await new FuncAwaitable<int>(() => 0); GetAwaiter() extension method As IAwaitable shows, all that an awaitable needs is just a GetAwaiter() method. In above code, FuncAwaitable<TResult> is created as a wrapper of Func<TResult> and implements IAwaitable<TResult>, so that there is a  GetAwaiter() instance method. If a GetAwaiter() extension method  can be defined for Func<TResult>, then FuncAwaitable<TResult> is no longer needed: public static class FuncExtensions { public static IAwaiter<TResult> GetAwaiter<TResult>(this Func<TResult> function) { return new FuncAwaiter<TResult>(function); } } So a Func<TResult> function can be directly awaited: int result = await new Func<int>(() => 0); Using the existing awaitable / awaiter - Task / TaskAwaiter Remember the most frequently used awaitable / awaiter - Task / TaskAwaiter. With Task / TaskAwaiter, FuncAwaitable / FuncAwaiter are no longer needed: public static class FuncExtensions { public static TaskAwaiter<TResult> GetAwaiter<TResult>(this Func<TResult> function) { Task<TResult> task = new Task<TResult>(function); task.Start(); return task.GetAwaiter(); // Returns a TaskAwaiter<TResult>. } } Similarly, with this extension method: public static class ActionExtensions { public static TaskAwaiter GetAwaiter(this Action action) { Task task = new Task(action); task.Start(); return task.GetAwaiter(); // Returns a TaskAwaiter. } } an action can be awaited as well: await new Action(() => { }); Now any function / action can be awaited: await new Action(() => HelperMethods.IO()); // or: await new Action(HelperMethods.IO); If function / action has parameter(s), closure can be used: int arg0 = 0; int arg1 = 1; int result = await new Action(() => HelperMethods.IO(arg0, arg1)); Using Task.Run() The above code is used to demonstrate how awaitable / awaiter can be implemented. Because it is a common scenario to await a function / action, so .NET provides a built-in API: Task.Run(): public class Task2 { public static Task Run(Action action) { // The implementation is similar to: Task task = new Task(action); task.Start(); return task; } public static Task<TResult> Run<TResult>(Func<TResult> function) { // The implementation is similar to: Task<TResult> task = new Task<TResult>(function); task.Start(); return task; } } In reality, this is how we await a function: int result = await Task.Run(() => HelperMethods.IO(arg0, arg1)); and await a action: await Task.Run(() => HelperMethods.IO());

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  • Design pattern for animation sequence in LibGDX

    - by kevinyu
    What design pattern to use for sequence of animation that involve different actor in libGDX. For example I am making a game to choose a wolf from a group of sheeps. The first animation played when the game begin is the wolf enter the field that is filled with two sheeps.Then the wolf disguise as a sheep and goes to the center of the screen. Then the game will shuffle the sheeps. After it finished it will ask the player where is the wolf. The game wait for player input. After that the game will show animation to show the player whether their answer is right or wrong. I am currently using State design pattern. There are four states wolfEnterState,DisguiseState,ShuffleState,UserInputState, and answerAnimationState. I feel that my code is messy. I use addAction with action sequence and action completion(new Runnable()) a lot. I feel that the action sequence is getting long. Is there a better solution for this kind of problem

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  • Am I missing a pattern?

    - by Ryan Pedersen
    I have a class that is a singleton and off of the singleton are properties that hold the instances of all the performance counters in my application. public interface IPerformanceCounters { IPerformanceCounter AccountServiceCallRate { get; } IPerformanceCounter AccountServiceCallDuration { get; } Above is an incomplete snippet of the interface for the class "PerformanceCounters" that is the singleton. I really don't like the plural part of the name and thought about changing it to "PerformanceCounterCollection" but stopped because it really isn't a collection. I also thought about "PerformanceCounterFactory" but it is really a factory either. After failing with these two names and a couple more that aren't worth mentioning I thought that I might be missing a pattern. Is there a name that make sense or a change that I could make towards a standardized pattern that would help me put some polish on this object and get rid of the plural name? I understand that I might be splitting hairs here but that is why I thought that the "Programmers" exchange was the place for this kind of thing. If it is not... I am sorry and I will not make that mistake again. Thanks!

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  • MVP Pattern Philsophical Question - Security Checking in UI

    - by Brian
    Hello, I have a philosophical question about the MVP pattern: I have a component that checks whether a user has access to a certain privilege. This privilege turns on or off certain UI features. For instance, suppose you have a UI grid, and for each row that gets bound, I do a security check to see if certain features in the grid should be enabled or disabled. There are two ways to do this: have the UI/view call the component's method, determine if it has access, and enable/disable or show/hide. The other is have the view fire an event to the presenter, have the presenter do the check and return the access back down to the view through the model or through the event arg. As per the MVP pattern, which component should security checks fit into, the presenter or the view? Since the view is using it to determine its accessibility, it seems more fitting in the view, but it is doing database checks and all inside this business component, and there is business logic there, so I can see the reverse argument too. Thoughts? Thanks.

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  • Confused about javascript module pattern implementation

    - by Damon
    I have a class written on a project I'm working on that I've been told is using the module pattern, but it's doing things a little differently than the examples I've seen. It basically takes this form: (function ($, document, window, undefined) { var module = { foo : bar, aMethod : function (arg) { className.bMethod(arg); }, bMethod : function (arg) { console.log('spoons'); } }; window.ajaxTable = ajaxTable; })(jQuery, document, window); I get what's going on here. But I'm not sure how this relates to most of the definitions I've seen of the module (or revealing?) module pattern. like this one from briancray var module = (function () { // private variables and functions var foo = 'bar'; // constructor var module = function () { }; // prototype module.prototype = { constructor: module, something: function () { } }; // return module return module; })(); var my_module = new module(); Is the first example basically like the second except everything is in the constructor? I'm just wrapping my head around patterns and the little things at the beginnings and endings always make me not sure what I should be doing.

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  • Looking for a better Factory pattern (Java)

    - by Sam Goldberg
    After doing a rough sketch of a high level object model, I am doing iterative TDD, and letting the other objects emerge as a refactoring of the code (as it increases in complexity). (That whole approach may be a discussion/argument for another day.) In any case, I am at the point where I am looking to refactor code blocks currently in an if-else blocks into separate objects. This is because there is another another value combination which creates new set of logical sub-branches. To be more specific, this is a trading system feature, where buy orders have different behavior than sell orders. Responses to the orders have a numeric indicator field which describes some event that occurred (e.g. fill, cancel). The combination of this numeric indicator field plus whether it is a buy or sell, require different processing buy the code. Creating a family of objects to separate the code for the unique handling each of the combinations of the 2 fields seems like a good choice at this point. The way I would normally do this, is to create some Factory object which when called with the 2 relevant parameters (indicator, buysell), would return the correct subclass of the object. Some times I do this pattern with a map, which allows to look up a live instance (or constructor to use via reflection), and sometimes I just hard code the cases in the Factory class. So - for some reason this feels like not good design (e.g. one object which knows all the subclasses of an interface or parent object), and a bit clumsy. Is there a better pattern for solving this kind of problem? And if this factory method approach makes sense, can anyone suggest a nicer design?

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  • Javascript Module pattern with DOM ready

    - by dego89
    I am writing a JS Module pattern to test out code and help me understand the pattern, using a JS Fiddle. What I can't figure out is why my "private methods" on line 25 and 26, when referenced via DOM ready, have a value of undefined. JSFiddle Code Sample: var obj = { key: "value" }; var Module = (function () { var innerVar = "5"; console.log("obj var in Module:"); console.log(obj); function privateFunction() { console.log("privateFunction() called."); innerFunction(); function innerFunction() { console.log("inner function of (private function) called."); } } function _numTwo() { console.log("_numTwo() function called."); } return { test: privateFunction, numTwo: _numTwo } }(obj)); $(document).ready(function () { console.log("$ Dom Ready"); console.log("Module in Dom Ready: "); console.log(Module.test()); });

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  • Question about modeling with MVC (the pattern, not the MS stuff / non web)

    - by paul
    I'm working on an application in which I'm looking to employ the MVC pattern, but I've come up against a design decision point I could use some help with. My application is going to deal with the design of state-machines. Currently the MVC model holds information about the machine's states, inputs, outputs, etc. The view is going to show a diagram for the machine, graphically allowing the user to add new states, establish transitions, and put the states in a pleasing arrangement, among other things. I would like to store part of the diagram's state (e.g. the x and y state positions) when the machine information is stored for later retrieval, and am wondering how best to go about structuring the model(s?) for this. It seems like this UI information is more closely related to the view than to the state-machine model, so I was thinking that a secondary model might be in order, but I am reluctant to pursue this route because of the added complexity. Adding this information to the current model doesn't seem the right way to go about it either. This is the my first time using the MVC pattern so I'm still figuring things out. Any input would be appreciated.

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  • Help with Abstract Factory Pattern

    - by brazc0re
    I need help with a abstract factory pattern design. This question is a continuation of: Design help with parallel process I am really confused where I should be initializing all of the settings for each type of medium (ex: RS232, TCP/IP, etc). Attached is the drawing on how I am setting up the pattern: As shown, when a medium is created, each medium imposes a ICreateMedium interface. I would assume that the Create() method also create the proper object, such as SerialPort serialPort = new SerialPort("COM1", baud); however, TCPIPMedium would have an issue with the interface because it wouldn't need to initialize a serial port object. I know I am doing something majorly wrong here. I just can't figure it out and have been stuck for a while. What I also get confused on show the interface IMedium will get access to the communication object once it is created so it can write out the appropriate byte[] packet. Any guidance would be greatly appreciated. My main goal is to have the Communicator class spit a packet out without caring which type of medium is active.

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  • doubleton pattern in C++

    - by benjamin button
    I am aware of the singleton pattern in C++. but what is the logic to get two instances of the object? is there any such pattern where we could easily get 2 pattern. for the logic i could think of is that i can change the singleton pattern itself to have two objects created inside the class.this works. but if the requirement grows like if i need only 3 or only 4 what is the deswign pattern that i could think of to qualify such requirement?

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  • Who benefits from the use of Design Patterns?

    Who benefits from the use of design patterns is like asking who benefits from clean air or a good education. All of the stakeholders of a project benefit from the use of design patterns. Project Sponsor Project sponsors benefit from the use of design patterns because they promote reduced development time which translates in to shorter project timelines and greater return on investment compared to other projects that do not make use of design patterns. Project Manager Project managers benefit from the use of design patterns because they reduce the amount of time needed to design a system, and typically the sub components of the system already have a proven track record. System Architect/Engineer System architects/engineers benefit from the use of design patterns because reduce the amount of time needed to design the core a system. The additional time is used to alter the design pattern through the use of innovative design and common design principles to adhere to the project’s requirements. Programmer Programmers benefit from the use of design patterns because they can reuse existing code already established by the design pattern and only have to integrate the changes outlined by the system architects/engineers. Tester Testers benefit from the use of design patterns because they can alter the existing test established for the design pattern to take in to account the changes made by the system architects/engineers. User Users benefit from the use of design patterns because the software is typically delivered sooner than projects that do not incorporate the use of design patterns, and they are assumed that the system will work as designed because it was based on a system that was already proven to work properly.

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  • Spawn a multi-threaded Java program from a Windows command line program, spawner won't end until spa

    - by Ross Patterson
    Short version: How can I prevent a spawned Java process in Windows from blocking the spawning process from ending? Long version: I'm trying to spawn a multi-threaded Java program (Selenium RC, not that it should matter) from a program launched from the Windows command line (NAnt's <exec> task, again, not that it should matter). I'm doing it using the Windows "start" command, and the spawned process is started and runs correctly. The spawning process receives control back and finishes (NAnt says "BUILD SUCCEEDED"), but doesn't actually exit to the command line. When the spawned process finally terminates (could be hours later), the command process returns and the command line prompt occurs. For example: <target name="start_rc"> <exec program="cmd" failonerror="false" workingdir="${ross.p5.dir}\Tools\selenium\selenium-server-1.0.1" verbose="true"> <arg value="/C"/> <arg value="start"/> <arg value="java"/> <arg value="-jar"/> <arg path="${ross.p5.dir}\Tools\selenium\selenium-server-1.0.1\selenium-server.jar"/> <arg value="-userExtensions"/> <arg path="${ross.p5.dir}\Tools\selenium\selenium-server-1.0.1\user-extensions.js"/> <arg value="-browserSideLog"/> <arg value="-log"/> <arg value="${ross.p5.dir}\artifacts\selenium.log"/> <arg value="-debug"/> </exec> </target> Produces: C :\Ross>nant start_rc NAnt 0.86 (Build 0.86.2898.0; beta1; 12/8/2007) Copyright (C) 2001-2007 Gerry Shaw http://nant.sourceforge.net Buildfile: file:///C:/Ross/ross.build Target framework: Microsoft .NET Framework 3.5 Target(s) specified: start_rc start_rc: [exec] Starting 'cmd (/C start java -jar C:\p5\Tools\selenium\selenium-server-1.0.1\selenium-server.jar -userExtensions C:\p5\Tools\selenium\selenium-server-1.0.1\user-extensions.js -browserSideLog -log C:\p5\artifacts\selenium.log -debug)' in 'C:\p5\Tools\selenium\selenium-server-1.0.1' BUILD SUCCEEDED Total time: 4.1 seconds. ... and then nothing until I close the window where Java is running, then ... C:\Ross> Obviously something is preventing the nant process from terminating, but shouldn't the Windows START command prevent that?

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  • How to change button background color depending on bound command canexecute ??

    - by LaurentH
    Hi, I Have a ItemTemplate in which is a simple button bound on a command, which can be executable or not depending on some property. I'd like the color of this button's background to change if the command isn't executable. I tried several methods, but I can't find anyway to do this purely in XAML (I'm doing this in a study context, and code behind isn't allowed). Here's my code for the button : <Button x:Name="Dispo" HorizontalAlignment="Center" Margin="0" VerticalAlignment="Center" Width="30" Height="30" Grid.Column="2" Grid.Row="0" Command="{Binding AddEmpruntCommandModel.Command}" CommandParameter="{Binding ElementName='flowCars', Path='SelectedItem'}" vm:CreateCommandBinding.Command="{Binding AddEmpruntCommandModel}" > <Button.Style> <Style TargetType="{x:Type Button}"> <Style.Triggers> <Trigger Property="IsEnabled" Value="True"> <Setter Property="Button.Background" Value="Green"/> </Trigger> <Trigger Property="IsEnabled" Value="False"> <Setter Property="Button.Background" Value="Red"/> </Trigger> </Style.Triggers> </Style> </Button.Style> </Button>

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  • How do you test a command object in a grails controller integration test?

    - by egervari
    I'm new to grails. How do I test a form command object to make sure that it's working? Here's some setup code in a test. When I try to do it, I get the following exceptions: Error occurred creating command object. org.codehaus.groovy.grails.web.servlet.mvc.exceptions.ControllerExecutionException: Error occurred creating command object. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) .... Caused by: groovy.lang.MissingPropertyException: No such property: password for class: project.user.RegistrationForm Possible solutions: password Here is my test case. As you can see, I set "password" on the params map... void testSaveWhenDataIsCorrect() { controller.params.emailAddress = "[email protected]" controller.params.password = "secret" controller.params.confirmPassword = "secret" controller.save() assertEquals "success", redirectArgs.view ... } Here's the controller action, that adds the command object as a closure parameter: def save = { RegistrationForm form -> if(form.hasErrors()) { render view: "create", model: [form: form] } else { def user = new User(form.properties) user.password = form.encryptedPassword if(user.save()) { redirect(action: "success") } else { render view: "create", model: [form: form] } } } Here's the command object itself... and note that it DOES have a "password" field... class RegistrationForm { def springSecurityService String emailAddress String password String confirmPassword String getEncryptedPassword() { springSecurityService.encodePassword(password) } static constraints = { emailAddress(blank: false, email: true) password(blank: false, size:4..10) confirmPassword(blank: false, validator: { password != confirmPassword }) } } I'm totally lost in the non-intuitive way to do controllers... Please help.

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  • How to open the command prompt and insert commands using Java?

    - by 404 Not Found
    There have been a few other questions on here sort of like this, but none seem to have any answers. Is it possible to open the command prompt (and I guess any other terminal for other systems), and execute commands in the newly opened window? Currently what I have is this: Runtime rt = Runtime.getRuntime(); rt.exec(new String[]{"cmd.exe","/c","start"}); I've tried adding the next command after the "start", I've tried running another rt.exec containing my command, but I can't find a way to make it work. If it matters, I'm trying to run a command similar to this: java -flag -flag -cp terminal-based-program.jar

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  • How can I modify command line in Ubuntu 10.04?

    - by user482594
    I am using a vpn service from certain server. I was given with a root account, and when I connect with a root account, the command line looks like below. root@xa9g82:/etc/# Then I used useradd to add an account called 'temp' When I connected to the server with temp, then the command line only has a single character. $ The user information is not shown, neither the path. Also, note that, in root's command line I can use tab to automatically complete the filename, however 'temp's command line inserts tab space, when I press tab. It is very inconvenient. I am using Ubuntu 10.04. How can I resolve this issue?

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  • A C# implementation of the CallStream pattern

    - by Bertrand Le Roy
    Dusan published this interesting post a couple of weeks ago about a novel JavaScript chaining pattern: http://dbj.org/dbj/?p=514 It’s similar to many existing patterns, but the syntax is extraordinarily terse and it provides a new form of friction-free, plugin-less extensibility mechanism. Here’s a JavaScript example from Dusan’s post: CallStream("#container") (find, "div") (attr, "A", 1) (css, "color", "#fff") (logger); The interesting thing here is that the functions that are being passed as the first argument are arbitrary, they don’t need to be declared as plug-ins. Compare that with a rough jQuery equivalent that could look something like this: $.fn.logger = function () { /* ... */ } $("selector") .find("div") .attr("A", 1) .css("color", "#fff") .logger(); There is also the “each” method in jQuery that achieves something similar, but its syntax is a little more verbose. Of course, that this pattern can be expressed so easily in JavaScript owes everything to the extraordinary way functions are treated in that language, something Douglas Crockford called “the very best part of JavaScript”. One of the first things I thought while reading Dusan’s post was how I could adapt that to C#. After all, with Lambdas and delegates, C# also has its first-class functions. And sure enough, it works really really well. After about ten minutes, I was able to write this: CallStreamFactory.CallStream (p => Console.WriteLine("Yay!")) (Dump, DateTime.Now) (DumpFooAndBar, new { Foo = 42, Bar = "the answer" }) (p => Console.ReadKey()); Where the Dump function is: public static void Dump(object options) { Console.WriteLine(options.ToString()); } And DumpFooAndBar is: public static void DumpFooAndBar(dynamic options) { Console.WriteLine("Foo is {0} and bar is {1}.", options.Foo, options.Bar); } So how does this work? Well, it really is very simple. And not. Let’s say it’s not a lot of code, but if you’re like me you might need an Advil after that. First, I defined the signature of the CallStream method as follows: public delegate CallStream CallStream (Action<object> action, object options = null); The delegate define a call stream as something that takes an action (a function of the options) and an optional options object and that returns a delegate of its own type. Tricky, but that actually works, a delegate can return its own type. Then I wrote an implementation of that delegate that calls the action and returns itself: public static CallStream CallStream (Action<object> action, object options = null) { action(options); return CallStream; } Pretty nice, eh? Well, yes and no. What we are doing here is to execute a sequence of actions using an interesting novel syntax. But for this to be actually useful, you’d need to build a more specialized call stream factory that comes with some sort of context (like Dusan did in JavaScript). For example, you could write the following alternate delegate signature that takes a string and returns itself: public delegate StringCallStream StringCallStream(string message); And then write the following call stream (notice the currying): public static StringCallStream CreateDumpCallStream(string dumpPath) { StringCallStream str = null; var dump = File.AppendText(dumpPath); dump.AutoFlush = true; str = s => { dump.WriteLine(s); return str; }; return str; } (I know, I’m not closing that stream; sure; bad, bad Bertrand) Finally, here’s how you use it: CallStreamFactory.CreateDumpCallStream(@".\dump.txt") ("Wow, this really works.") (DateTime.Now.ToLongTimeString()) ("And that is all."); Next step would be to combine this contextual implementation with the one that takes an action parameter and do some really fun stuff. I’m only scratching the surface here. This pattern could reveal itself to be nothing more than a gratuitous mind-bender or there could be applications that we hardly suspect at this point. In any case, it’s a fun new construct. Or is this nothing new? You tell me… Comments are open :)

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  • Command line tool to write flac, ogg vorbis and mp3 id3v2 tags?

    - by burzum
    Is there any command line tool that can write all three formats/containers? I've already searched but could not find anything that does the job. So far I'm using vorbiscomment, metaflac and id3tool and I really would like to replace them by a single tool if possible. If there is no tool than can write them all, is there at least any suggestion to replace id3tool with something that can write id3v2 (v2.4) tags at least? I'm not looking for a tagger but for a tool that will allow me to write meta data by a script to the different audio files. My current status is that I have a script that uses the three tools (vorbiscomment, metaflac and id3tool) but then i realized that id3tool can not write id3v2 tags... I'm creating automatically these 3 audio formats from a wav master and need to be able to automate the meta data writing to these files.

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  • SQL like group by and sum for text files in command line?

    - by dnkb
    I have huge text files with two fields, the first is a string the second is an integer. The files are sorted by the first field. What I'd like to get in the output is one line per unique string and the sum of the numbers for the identical strings. Some strings appear only once while other appear multiple times. E.g. Given the sample data below, for the string glehnia I'd like to get 10+22=32 in the result. Any suggestions how to do this either with gnuwin32 command line tools or in linux shell? Thanks! glehnia 10 glehnia 22 glehniae 343 glehnii 923 glei 1171 glei 2283 glei 3466 gleib 914 gleiber 652 gleiberg 495 gleiberg 709

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