PowerShell Looping: Understanding and Using Do…While

Summary: Microsoft Scripting Guy, Ed Wilson, talks about using the Do…While statement in Windows PowerShell scripts.

Microsoft Scripting Guy, Ed Wilson, is here. Last week, the Scripting Wife and I were at the Windows PowerShell Summit in Bellevue, Washington. It was an awesome week. We got to reconnect with many old friends, and we also made new ones. I delivered three sessions on Wednesday. Needless to say, I was a bit tired. In fact, the entire week was tiring. I am talking about 16-hour days, and a three-hour time zone change kind of tired. But the energy was buzzing around; and therefore, it was awesome.

Before one of my sessions, I decided to get a cup of coffee. Someone saw me and said, “What are you doing with coffee? Don’t you usually drink tea?” Well, yes I do, but I thought I would go for the «hard stuff» to provide a little extra jolt before my session.

After one of my sessions, someone came up to me and said they liked my blog posts last week, and wondered if I would write something about Do. A «Scooby Do, where are you» kind of do? Probably not. Here you go…

The Do…While loop construction in Windows PowerShell is a bottom evaluated version of the While loop that I talked about in PowerShell Looping: Using While. The whole idea is that I am going to do something while a condition exists. As an example, here is a recent weather forecast for Charlotte, North Carolina, where the Scripting Wife and I live:

So I might go outside and ride my bike while the sun is shining. The strange thing is the way the evaluation goes. It might look like this:

Go to the garage.

Ride while it is sunny.

The evaluation occurs at the end. In Windows PowerShell script, it would look like the following:

> (While (weather –eq ‘sunny’)

Using Do…While

Now I want to take a look at a real Windows PowerShell script that illustrates using the Do…While loop.

In the script that follows, I set the value of the $a variable to equal 1. In the Do loop, I print a message that I am starting the loop. Next I display the value of $a, and then I increment $a. I print the current value of $a, and then close the script block. In the While evaluation block, I check to see if $a is less than or equal to 5. The script is shown here:

«Starting Loop $a»

The script in the ISE and the output from the script are shown in the following image:

So, I can see that there are four parts to a Do…While loop. First is the Do keyword, then the script block that I want to “do.” Then comes the While keyword, and the condition that is evaluated to determine if another loop will occur.

In many respects, the While statement and the Do…While loop are similar. The difference is that with the While statement, the condition is evaluated to determine if the script block will take place. In the Do…While loop, because the condition occurs at the end of the loop, it will always loop at least once.

This is illustrated in the image that follows. I use exactly the same script as I used previously, but instead of setting the value of $a, I assign a value of 9. Now, 9 is greater than 5, so the ($a –le 5) condition is never true. Yet, as you can see in the image, the script block ran once.

A more practical example

I decided to write a little script that will monitor for the existence of a process by name. As long as the process runs, the script continues to loop around. To ensure that the process runs, I start it at the beginning of the script. I then use the –contains operator to look for the process by name in the control portion of the loop. Here is the script:

«$p found at $(get-date)»

> While ($proc.name -contains ‘notepad’)

In the following image, I see that it took me a few seconds to close Notepad. When I manually close Notepad, the looping stops.

Windows PowerShell Fundamentals Week will continue tomorrow when I will continue talking about looping.

Как выполнить цикл loop определенное кол-во раз ?

Выполнить определенное кол-во раз, если событие произошло
Всем привет, подскажите как бы сделать чтобы скрипт, чтобы он выполнялся определенное кол-во раз.

Как подсчитать кол-во запусков приложения и выполнить определенное условие?
Всем привет! Есть задача — после 10 запусков приложения выполнить некоторое действие. Вроде как с.

Как в цикле выполнить определенное действие один раз?
for (int i = 0; i 3

Сделает 10 шагов (c 0 по 9).

А можно и через for:

А будет ли он в том же окне выполнять команды после например 3 цикла ?
выполнил он цикл заданное количество раз и выполняет нижеследующие команды

Добавлено через 35 минут
Сделал вот так . мб есть лучше решение

froa, вложить один цикл можно в другой.

Заказываю контрольные, курсовые, дипломные и любые другие студенческие работы здесь или здесь.

Как сделать так, чтобы цикл выполнялся определенное количество раз в Pascal?
Нужно сделать так, чтобы пользователь ввел какое-то число и цикл выполнился такое число раз.

Создать цикл, повторяющийся раз в определенное время
Здравствуйте, подскажите, как создать цикл, который выполняется раз в определенное время( к примеру.

Создать цикл, который будет повторяться через определенное количество раз
Как в delphi начать цикл который будет повторятся через определенное колличество раз

Выполнить цикл while указанное количество раз
привет ,как сделать так чтобы цикл количество равное число. то есть while(3)< ну нужно.

Do. Оператор Loop Do. Loop statement

Повторяет блок операторов, пока условие имеет значение True или пока условие не примет значение True. Repeats a block of statements while a condition is True or until a condition becomes True.

Синтаксис Syntax

Do [< while | until > условие ] Do [< While | Until > condition ]
[ Операторы ] [ statements ]
[ Exit Do ] [ Exit Do ]
[ Операторы ] [ statements ]
CNAME Loop

Также можно использовать следующий синтаксис. Or, you can use this syntax:

Do Do
[ Операторы ] [ statements ]
[ Exit Do ] [ Exit Do ]
[ Операторы ] [ statements ]
Loop [ время | до > условие ] Loop [< While | Until > condition ]

Синтаксис оператора Do Loop состоит из следующих элементов. The Do Loop statement syntax has these parts:

Часть Part	Описание Description
установлен condition	Необязательно. Optional. Числовое выражение или строковое выражение, разрешаемое в значение True или False. Numeric expression or string expression that is True or False. Если Condition имеет значение NULL, условие считается ложным. If condition is Null, condition is treated as False.
Операторы statements	Один или несколько операторов, которые повторяются, пока условие имеет значение true. One or more statements that are repeated while, or until, condition is True.

Примечания Remarks

Любое количество операторов Exit Do можно поместить в любом месте оператора Do. Loop в качестве альтернативного способа выхода из оператора Do. Loop. Any number of Exit Do statements may be placed anywhere in the Do…Loop as an alternate way to exit a Do…Loop. Exit Do часто используется после оценки некоторого условия, например If. Затем, в этом случае оператор Exit Do передает управление оператору, следующему сразу за циклом. Exit Do is often used after evaluating some condition, for example, If…Then, in which case the Exit Do statement transfers control to the statement immediately following the Loop.

При использовании во вложенных циклах Do…Loop оператор Exit Do передает управление циклу, который находится на один уровень выше цикла оператора Exit Do. When used within nested Do…Loop statements, Exit Do transfers control to the loop that is one nested level above the loop where Exit Do occurs.

Пример Example

В этом примере показано использование операторов Do. Loop. This example shows how Do. Loop statements can be used. Внутренняя процедура Do. Loop выполняет циклы 10 раз, запрашивает пользователя, если он должен продолжить работу, устанавливает значение флага false при выборе значения нети преждевременно завершает работу с помощью оператора Exit Do . The inner Do. Loop statement loops 10 times, asks the user if it should keep going, sets the value of the flag to False when they select No, and exits prematurely by using the Exit Do statement. Выход из внешнего цикла происходит сразу после проверки значения флага. The outer loop exits immediately upon checking the value of the flag.

См. также See also

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How to do a for loop in windows command line?

I was wondering if this was possible? I’m not familiar with using windows command line, but I have to use it for a project I’m working on. I have a a number of files, for which I need to perform a function for each. I’m used to working with python, but obviously this is a bit different, so I was hoping for some help.

Basically I need the for loop to iterate through 17 files in a folder, perform a function on each (that’s using the specific software I have here for the project) and then that will output a file with a unique name (the function normally requires me to state the output file name) I would suck it up and just do it by hand for each of the 17, but basically it’s creating a database of a file, and then comparing it to each of the 17. It needs to be iterated through several hundred times though. Using a for loop could save me days of work.

3 Answers 3

The commandline interpreter does indeed have a FOR construct that you can use from the command prompt or from within a batch file.

For your purpose, you probably want something like:

Which will result in the name of each file with extension *.ext in the current directory being passed to my-function (which could, for example, be another .bat file).

The (*.ext) part is the «filespec», and is pretty flexible with how you specify sets of files. For example, you could do:

To perform an operation in a different directory.

There are scores of options for the filespec and FOR in general. See

from the command prompt for more information.

Unix / Linux — Shell Loop Types

In this chapter, we will discuss shell loops in Unix. A loop is a powerful programming tool that enables you to execute a set of commands repeatedly. In this chapter, we will examine the following types of loops available to shell programmers −

You will use different loops based on the situation. For example, the while loop executes the given commands until the given condition remains true; the until loop executes until a given condition becomes true.

Once you have good programming practice you will gain the expertise and thereby, start using appropriate loop based on the situation. Here, while and for loops are available in most of the other programming languages like C, C++ and PERL, etc.

Nesting Loops

All the loops support nesting concept which means you can put one loop inside another similar one or different loops. This nesting can go up to unlimited number of times based on your requirement.

Here is an example of nesting while loop. The other loops can be nested based on the programming requirement in a similar way −

Nesting while Loops

It is possible to use a while loop as part of the body of another while loop.

Syntax

Example

Here is a simple example of loop nesting. Let’s add another countdown loop inside the loop that you used to count to nine −

This will produce the following result. It is important to note how echo -n works here. Here -n option lets echo avoid printing a new line character.