I like how my assumption that Part IV of Write Functions, Not Scripts wouldn’t be a worthy contender to the previous three parts (P1, P2, P3). Seriously, I didn’t think it compared, and if I’m not mistaken, it’s been the most popular post in this series thus far.

It’s a simple concept though: short, simple, single-purposed is sufficient for writing functions. Think small, easier to troubleshoot code. Say you have five functions that run in succession — one right after the other. The point at which things break will likely remove 4 of the 5 functions as areas you even need to review. That means you’re troubleshooting a fifth of the code the scriptwriter would have to review. Functions are a no-brainer. Well, they ought to be, anyway.

Time for some more thoughts on why functions over scripts. Hey, ever see one of these in a script?

$UserCount = 10
# When using in production, please comment out the above line.
# Then, uncomment the below line.
# $UserCount = 20

This is why we have a Read-Host. This, would be better.

$UserCount = Read-Host -Prompt 'Enter the preferred User Count'

Before blogging was my main gig, you might find me scouring various forums more often and helping others (and secretly learning more, too). A good number of people were getting their input via the Read-Host cmdlet. It’s nice and all, but by itself, there’s a bit of mystery as to what a user might enter. While I’m expecting 10, or 20, I could end up with all kinds of obnoxious values.

$UserCount = Read-Host -Prompt 'Enter the preferred User Count'
Enter the preferred User Count: DogCatMom5
# Huh!?

Inside a Do loop construct, we can better control the acceptable input.

Do {
    $UserCount = Read-Host -Prompt 'Enter the preferred User Count'
} Until ($UserCount -eq 10 -or $UserCount -eq 20)
Enter the preferred User Count: 1
Enter the preferred User Count: 2
Enter the preferred User Count: 3
Enter the preferred User Count: 4
Enter the preferred User Count: 5
Enter the preferred User Count: 6
Enter the preferred User Count: DogCatMom5
Enter the preferred User Count: 10

But there’s still a better way. Function’s allow for parameters and so, as absolutely as best as we can, we need to separate our lives — and our function writing — from Read-Host. If it’s ever in a function, and I’ll agree that it can happen, there ought to be really great reason as to why. We’ll close out today’s post with a simple function example that uses parameters. This is such a huge benefit.

Function Test-ParamsInAFunction {
    Param (
        $Number,
        $Letter
    )
 
    If ($Number -and $Letter) {
        Write-Output -InputObject "You have entered the number $Number, and the letter $Letter."
    } ElseIf ($Number) {
        Write-Output -InputObject "You have entered the number $Number."
    } ElseIf ($Letter) {
        Write-Output -InputObject "You have entered the letter $Letter."
    } Else {
        Write-Output -InputObject "You have not entered a number or letter."
    }
}

Test-ParamsInAFunction
Test-ParamsInAFunction -Number 5
Test-ParamsInAFunction -Letter X
Test-ParamsInAFunction -Number 10 -Letter D

You have not entered a number or letter.
You have entered the number 5.
You have entered the letter X.
You have entered the number 10, and the letter D.

Functions can handle run time delivered values. There’s no more opening up scripts and adding and removing static comments and variable assignments. There’s no using Read-Host inside our scripts and functions (unless, again, you’ve got a really great reason), even if, you’re using a language construct to protect the acceptable values. Before we full on wrap up, let me show you how to make a parameter only accept the 10 and 20 values.

Function Test-ParamsInAFunction {
    Param (
        [ValidateSet(10,20)]
        $Number
    )
    ...
}

See you again next time.

If you haven’t been with us in the previous three posts (this one, this one, and this one), we’ve been discussing why functions, over scripts. If you haven’t already, it’s time to change your mindset.

The idea is to write small, concise, single-purposed, chunks of code. We call these functions. What we don’t need… is long, overly complex, multi-purposed scripts. We’ve got to stop the scripting mentality. You know the one… you’re writing a script and your next thought is, now I need to do this…and then you write lines and lines beneath that which has already written. Now you have a multipurpose script and no clear end in sight.

It’s pretty simple: the longer the script, the more pieces to troubleshoot and when adding new features, the more potential areas to make errors. You’re creating more confusion. The whole process of script writing can easily and quickly get away from you. In one moment you add one solution, and then in another, you add more solutions to other problems you want to solve, and it’s all in a single file. Ugh.

That was it. Start writing in a single purposed methodology. Even if you’re not going not to write in functions beginning tomorrow morning, like you should, start scripting in single purposed scripts. If you need it, make that your first step. I’m not writing for my own benefit this evening; I’m writing for yours. You’re going to love being a function writer. You just need to make this the week you start, if you haven’t already. Here, I’ll get you started:

Function Get-ItDone {
    # Add your code here.
}
Get-ItDone

Alright, see you next time.

First off, I have to say, the first two posts in this series have been very successful. Nearly 200 visitors on a Saturday and then a Sunday, too — that’s unheard of during the weekend. And to think, these two posts: Part I and Part II, have felt like some of the most distracted and unpredictable writing of mine to date, and I’ve been at this for almost four years straight, without a missed month.

Okay, to continue with a distraction, in Write Functions, Not Scripts — Part II, I showed a picture of the fog on my cul-de-sac in Tucson, AZ (the desert) last Friday. Here’s that picture now. That fog, is not typical for us. Maybe it happens once a year.

I mentioned that I’d include the typical view, and so here’s a picture from Saturday — just one day later. And that’s, what it normally looks like around here.

Moving along, as if there’s a PowerShell related topic at hand. So, here’s one reason for functions, over scripts: it’s variables. Let’s move out the fog, and explain.

When we’re developing scripts, we often create variables and assign them values at the top of our code. Normal stuff. The problem is that when we go to execute the script a second (or third, or fourth) time, the variables in our script have already been assigned a value, and that may make our results incorrect. This can lead to confusion and wasted time, incorrect results, and extra lines of unnecessary commands to initialize variables. Stop initializing, and then re-initializing, variables.

Let’s take a look at an example.

In each pass though the below ForEach-Object cmdlet, we set the $User variable to my name with the number of the current pass at the end. Then, we increase the $Count variable by 1. Take a look at the below results. Everything looks perfect. My name includes the current iteration through the loop, and the count matches, as it should.

1..5 | ForEach-Object {
    $User = "tommymaynard$_"
    $Count++

    "Count: $($Count)"
    "User: $User"
}

Count: 1
User: tommymaynard1
Count: 2
User: tommymaynard2
Count: 3
User: tommymaynard3
Count: 4
User: tommymaynard4
Count: 5
User: tommymaynard5

Now, let’s run it again.

1..5 | ForEach-Object {
    $User = "tommymaynard$_"
    $Count++

    "Count: $($Count)"
    "User: $User"
}

Count: 6
User: tommymaynard1
Count: 7
User: tommymaynard2
Count: 8
User: tommymaynard3
Count: 9
User: tommymaynard4
Count: 10
User: tommymaynard5

We didn’t want to continue to increase the $Count variable past five, but because we’re scripting, we did it anyway. Writing something like this would required a Remove-Variable, or Clear-Variable command, when the final loop was done. Annoying, and without it, when you’re scripting, you’re going to have inaccuracies.

With functions, we don’t ever need to reinitialize variables to their default values. And of course, we don’t need to remove them, or clear them, before our code is run a second, or third time. This isn’t to say you’ll never change the value of a variable inside a function, it’s to say that variables in a function don’t typically exist before, or after, a function is executed.

Function Show-CountAndUser {
    1..5 | ForEach-Object {
        $User = "tommymaynard$_"
        $Count++

        "Count: $($Count)"
        "User: $User"
    }
}

PS > Show-CountAndUser
Count: 1
User: tommymaynard1
Count: 2
User: tommymaynard2
Count: 3
User: tommymaynard3
Count: 4
User: tommymaynard4
Count: 5
User: tommymaynard5

Okay, that was the first execution. One through five: it looks good. And here’s, the second execution.

PS > Show-CountAndUser
Count: 1
User: tommymaynard1
Count: 2
User: tommymaynard2
Count: 3
User: tommymaynard3
Count: 4
User: tommymaynard4
Count: 5
User: tommymaynard5

Ah, perfect! Write functions, and stop worrying about having to set, and reset, variables. Use the variable scope provided by functions — it wants to help you. It’s one reason for functions over scripts. Back again later.

Part IV is now available.