Topic: Reusable Code II

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

In today’s PSMonday, we’ll jump right back into calculated properties, as we continue to create some reusable code. Last week our final addition was to use a calculated property to modify the name of a property, as can be seen below. We took its default value of “Name,” and changed it to “Process Name.”

Get-Process -Name powershell_ise |
    Select-Object -Property @{Name='Process Name';Expression={$_.Name}},Description,Company,WorkingSet,PrivateMemorySize

Today we’ll add two more calculated properties, but before we do, let’s reformat this code a bit, so it fits better. First, we’re going to use “N” instead of Name and “E” instead of Expression, for the keys in our calculated property hash table. Second, we’ll take advantage of the commas between our  properties which allows each of them to sit on their own line. We could have put a space after each comma and left them on the same line as the first property, and it would have wrapped them for us; however, we’re about to add those other calculated properties.

Get-Process -Name powershell_ise |
    Select-Object -Property @{N='Process Name';E={$_.Name}},
        Description,
        Company,
        WorkingSet,
        PrivateMemorySize

The WorkingSet and PrivateMemorySize values are being reported in bytes. Let’s modify that, beginning with the WorkingSet property. Take a look at the newest changes, and we’ll discuss them after the example and its results.

Get-Process -Name powershell_ise |
    Select-Object -Property @{N='Process Name';E={$_.Name}},
        Description,
         Company,
        @{N='Shared Memory';E={"$([Math]::Round($_.WorkingSet / 1MB)) MB"}},
        PrivateMemorySize

Process Name      : powershell_ise
Description       : Windows PowerShell ISE
Company           : Microsoft Corporation
Shared Memory     : 420 MB
PrivateMemorySize : 405536768

As you can see in the above example, we first changed the term “WorkingSet” to “Shared Memory.” This time, however, we also modify the value it displays using the Expression key-value pair. We won’t go into this too deep, other than to say we first, divided our Working Set value by 1 MB, as we wanted to report our values in megabytes. Second, we directly accessed .NET to round our value using a Round method, and finally, we added the string “MB” to the end of the value to make it clear what measurement we’re using.

Next, we’ll add a third calculated property, but this time to the PrivateMemorySize property. This will allow it to function just like the modified WorkingSet property. As you can likely tell, I’ve used more lines than is necessary, in order that this best fits.

Get-Process -Name powershell_ise |
    Select-Object -Property @{N='Process Name';E={$_.Name}},
        Description,
        Company,
        @{N='Shared Memory';E={"$([Math]::Round($_.WorkingSet / 1MB)) MB"}},
        @{N='Private Memory Size';
            E={"$([Math]::Round($_.PrivateMemorySize / 1MB)) MB"}}

Process Name        : powershell_ise
Description         : Windows PowerShell ISE
Company             : Microsoft Corporation
Shared Memory       : 420 MB
Private Memory Size : 387 MB

Okay, let’s stop here and pick up from this point next Monday.

Topic: Reusable Code I

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

After I type the same thing a few times, and suspect I’ll need, or want, to continue to do that, I’ll typically write a function for it, so that I never have to type it again. That’s the purpose of a function. It’s a container for a series of commands that I can run, or invoke, simply by entering its name. Today we’ll start a four-part PSMonday on how to reuse code from beginning to end. As we close up PSMonday, these last several are going to be the ones in which to really pay attention.

Let’s start by entering a simple, Get-Process command, in order to determine whether or not the PowerShell ISE — the PowerShell Integrated Scripting Environment — is currently running.

Get-Process -Name powershell_ise | Select-Object -Property ProcessName,Id

ProcessName      Id
-----------      --
powershell_ise 5732

In the above example, we used Select-Object to filter the properties that are returned by Get-Process. The ISE is running, otherwise we would’ve received an error, indicating that the process could not be found.

Next, let’s pipe the results of an unfiltered, Get-Process command to a mildly modified Get-Member command, and take a look at all the properties of the returned object.

Get-Process -Name powershell_ise | Get-Member -MemberType Property

Here’s another filtered Get-Process command, that only includes the properties that hold information in which I am interested.

Get-Process -Name powershell_ise |
    Select-Object -Property Name,Description,Company,WorkingSet,PrivateMemorySize

Name              : powershell_ise
Description       : Windows PowerShell ISE
Company           : Microsoft Corporation
WorkingSet        : 162627584
PrivateMemorySize : 153522176

Let’s make a change to the Name property using what’s called a calculated property. Among other things, a calculated property allows us to rename a property’s default name to something else.

Get-Process -Name powershell_ise |
    Select-Object -Property @{Name='Process Name';Expression={$_.Name}},Description,Company,WorkingSet,PrivateMemorySize

Process Name      : powershell_ise
Description       : Windows PowerShell ISE
Company           : Microsoft Corporation
WorkingSet        : 162324480
PrivateMemorySize : 153812992

The calculated property looks like this, when it’s all by itself.

@{Name='Process Name';Expression={$_.Name}}

Notice in the above results that Name property is now named, Process Name. The calculated property consists of a hash table, as signified by @{}, that contains two, key-value pairs. One pair includes the Name key, and the second key-value pair includes an Expression key. We’ll continue next week with some additional examples of calculated properties, as we continue to learn about creating reusable code.

Topic: Do-Until

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

I said I would say it this week too, so let’s get it out of the way: The Do-While and Do-Until loops ensure that the statement list is run at least once. Your code is going to execute at least one time using a Do construct. This is because the condition, that determines whether or not we loop again, isn’t evaluated until the statement list has run once. If you need to ensure your code executes at least one time, then the Do-While and Do-Until variations of the Do loop, may be the language construct you need.

Here’s the conceptual examples of the Do-Until.

Do {<statement list>} Until (<condition>)

Do {
    <statement list>

} Until (<condition>)

Our first below example should look somewhat familiar. We saw it first last week in the Do-While examples. We assign 1 to the $Number variable and then enter the Do loop. We output a string statement and then increment the $Number variable. Then, we check the condition. The condition indicates that we’ll continue to loop until $Number is less than 10. Well, 1 is always less than 10, so we exit the construct. This is a clear example that we always run the statement list at least once in a Do loop, before we check the condition.

$Number = 1

Do {
    Write-Output -InputObject "In the Do loop ($Number)."
    $Number++

} Until ($Number -lt 10)

In the Do loop (1).

Let’s modify this example. We’ll reinitialize the $Number variable back to 1 and start again. This time our condition states that we’ll continue to loop until $Number is greater than 10. As $Number is lower, you can likely guess that we’re going to run through this loop several times. Ten times, to be exact.

$Number = 1

Do {
    Write-Output -InputObject "In the Do loop ($Number)."
    $Number++

} Until ($Number -gt 10)

In the Do loop (1).
In the Do loop (2).
In the Do loop (3).
In the Do loop (4).
In the Do loop (5).
In the Do loop (6).
In the Do loop (7).
In the Do loop (8).
In the Do loop (9).
In the Do loop (10).

In closing out the Do variations, we’ll add a final example. Much like last week, we’ll transition from using numeric values to date times. In this example, we’ll add 10 seconds to the current time. Then, we’ll output a string value and sleep (pause) for a second. Eventually, the current time will be greater than the time when we began; therefore, the condition will be $true and we’ll exit the looping construct.

$Time = (Get-Date).AddSeconds(10)

Do {
    Write-Output -InputObject 'Waiting for time to pass...'
    Start-Sleep -Seconds 1

} Until ((Get-Date) -ge $Time)

Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...
Waiting for time to pass...

Next week is our final language construct — the While loop. By then, you’ll have a full and complete understanding of the various control structures we can use to respond to conditions in PowerShell. In case you hadn’t considered it, learning these concepts — even if it’s with PowerShell — is going to make learning other scripting, and even programming languages, easier to do.

Topic: Do-While

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

Next up on our language construct journey, is part one of the Do loop: the Do-While. Once you’ve read this week’s, and next week’s PSMonday, be sure to read the full about help topic using the below command.

Get-Help -Name about_Do -ShowWindow

Here’s a couple conceptual examples of the Do-While loop. Of the two, you’ll see me use the second example, in order that my code is easier to read.

Do {<statement list>} While (<condition>)

Do {
    <statement list>

} While (<condition>)

For our first example, we’ll start looping based on the value of a variable. We begin by assigning the numeric value of 1 to the $Number variable. This assignment is done outside of the looping construct. Once set, we begin the loop. On the first pass, we indicate that we’re in the loop, as well as the current value of the $Number variable, we then increase the value of the $Number, and then we check if it is less than (-lt) the numeric value of 10. While this condition is true, we’ll continue to loop, incrementing the value in $Number each time, until the value in $Number variable is no longer less than 10.

$Number = 1

Do {
    Write-Output -InputObject "In the Do loop ($Number)."
    $Number++

} While ($Number -lt 10)

In the Do loop (1).
In the Do loop (2).
In the Do loop (3).
In the Do loop (4).
In the Do loop (5).
In the Do loop (6).
In the Do loop (7).
In the Do loop (8).
In the Do loop (9).

Instead of using a numeric value condition, this time, we’ll use a datetime object instead. Take a look at this next example, and then follow the further below description of each task within the example.

"Current Time: $((Get-Date).ToString())"

$Time = (Get-Date).AddSeconds(10)

"Future Time : $($Time.ToString())"

Do {
    Write-Output -InputObject '--> Waiting for time to pass.'
    (Get-Date).ToString()
    Start-Sleep -Seconds 1

} While ((Get-Date) -lt $Time)

"Current Time: $((Get-Date).ToString())"

Current Time: 1/29/2017 1:46:20 PM
Future Time : 1/29/2017 1:46:30 PM
--> Waiting for time to pass.
1/29/2017 1:46:20 PM
--> Waiting for time to pass.
1/29/2017 1:46:21 PM
--> Waiting for time to pass.
1/29/2017 1:46:22 PM
--> Waiting for time to pass.
1/29/2017 1:46:23 PM
--> Waiting for time to pass.
1/29/2017 1:46:24 PM
--> Waiting for time to pass.
1/29/2017 1:46:25 PM
--> Waiting for time to pass.
1/29/2017 1:46:26 PM
--> Waiting for time to pass.
1/29/2017 1:46:27 PM
--> Waiting for time to pass.
1/29/2017 1:46:28 PM
--> Waiting for time to pass.
1/29/2017 1:46:29 PM
Current Time: 1/29/2017 1:46:30 PM

We began the above example by echoing the current date and time. Then we created the $Time variable and made use of the AddSeconds() method to store the date and time 10 seconds into the future. So we know that time, we echoed it to the screen, as well.

Next, we entered the Do-While construct. Our statement list included writing a string to indicate that we we’re waiting for time to pass, writing the current date and time, and then sleeping for one second. Once these commands were completed, we checked the current date and time as a part of the Do-While’s condition. If the current time was still less than (-lt) ten seconds in the future from when we started ($Time), then we looped again. When that condition was eventually met — when the current time was no longer less than that future time — we exited the Do-While statement and echoed the current time.

We’ll cover the Do-Until next week — a language construct variation that you should probably already be able to figure out based on today’s PSMonday. I’ll say it today and next Monday, as well: The Do loops — both Do-While and Do-Until — ensure that we’ll go through the statement list at least one time. This is to say, that the condition is not evaluated until your code has been executed at least once.

Topic: For

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

This week we’ll discuss the For loop. The first of the two below commands can be used to open the For help file. Inside the file you’ll find the command layout, as we’ve seen with the other language constructs, and cmdlets. The way I write the For language construct, has been included below.

Get-Help -Name about_For -ShowWindow

For (<init>; <condition>; <repeat>) {
    <statement list>
}

The For loop begins with the For keyword and a set of parenthesis. Inside the parenthesis is an initialization (listed as init above), followed by a semi-colon. Following the initialization, we include a condition. By now, you undoubtedly realize there will always be some sort of required condition within our language constructs. Foll­owing the second semi-colon, we have a way to increment our initialization variable, as an assurance we’ll loop through the For loop as many times as is indicated by our condition. This may make more sense, very shortly.

We’re only going to look at a single example for the For loop, but we’ll be sure to highlight all the key features, as well as fully walk through the example. Take a look at the below example, and then we’ll discuss it thoroughly.

For ($i = 1; $i -le 10; $i++) {
    "The value of the `$i variable is $i."
    Start-Sleep -Seconds 1
}

We begin our For statement by entering the For keyword, followed by a set of parenthesis. To initialize the For construct, we’ll set a variable, $i, to the numeric value of 1, as $i = 1. We could have used a different number, however, it would require some changes in the areas we’ll discuss next. We could’ve use a different variable, too, had we opted to do so.

Our condition, $i -le 10, indicates to continue to loop through this For construct, so long as $i is less than, or equal to, 10. The final value in the parenthesis, $i++, increments the value in $i by 1, for each loop iteration. It’s shorthand for $i = $i + 1. Inside the curly brackets is where we enter our statement(s); this is where we do our work. In our example, we’ll echo a string that includes the value of the $i variable, and then sleep, or pause, for one second. Here’s the results of our example.

The value of the $i variable is 1.
The value of the $i variable is 2.
The value of the $i variable is 3.
The value of the $i variable is 4.
The value of the $i variable is 5.
The value of the $i variable is 6.
The value of the $i variable is 7.
The value of the $i variable is 8.
The value of the $i variable is 9.
The value of the $i variable is 10.

There’s some confusion about when to use a foreach variation (foreach and ForEach-Object), and the For construct. I use For when I know how many times I need to loop, as this is a requirement. If you know this piece of information, then you might consider the For loop over the other two looping constructs we’ve discussed thus far. Think back to foreach and ForEach-Object: the number of times we were going to loop, was never a consideration before we began.

We’ll be back next Monday where we’ll cover another looping construct: the Do-While loop.