Understanding $args in PowerShell

scottalanmiller

Oh, I have an idea.

Think of my way of doing $args as being like MadLibs. But you just give a string of words and they get put in in order. Your program or script is like a MadLibs where you feed it the list of words and it says funny things. In fact, making an actual MadLibs script is a common and fun scripting project to do for exactly this reasons.

Now Martin's way is more like MadLibs where you know some basics like name, age, color, size, etc. and you put in words associated with those things so that you get a simpler matching of words to where they are used.

The approach that I am demonstrating is just taking things in order one after another. His is to identify what they are and label them so that they are more useful. Both are important to understanding, but one after another. In the real world of script writing his approach is way, way more common and practical. Not every single time, but the vast majority. But understanding my way first is important because you need to know what is happening.

Martin9700

@scottalanmiller said:

for ($i=0; $i -lt $args.length; $i++) {
'This is $args[' + $i + "], which is: " + $args[$i]
}

This could also be written:

for ($i=0; $i -lt $args.length; $i++) {
  "This is `$args[$i], which is: $($args[$i])"
}

scottalanmiller

That's a little better I'm a BASH, Python and Ruby guy, I don't really write PowerShell normally

chutestrate

You guys are right about needing to understand arrays better i guess. I just started this last week, and thought i had at least a slight understanding of it. I can follow the scripting commands in the first line, but what is the second line doing?

At least i can make ps1 files, and get it into powershell, lol

scottalanmiller

@chutestrate said:

I can follow the scripting commands in the first line, but what is the second line doing?

The second line is just printing out the name of the argument that we are on and what the value of that argument is for you to see. When you look at the output you can see it patch up. You get to see the name of the argument like $args[0] and the value held by that argument.

scottalanmiller

An array, as we discussed via PM, is an "array of things", like a list. As we are programming here, that is really a list of variables. So in the same way that a normal variable can have something in it such as a string, so can an individual array element. Here is an example:

$myname = "John"

or as a single element array:

$myarray[0] = "John"

These two things accomplish basically the same thing. You have stored your name in a variable. Now what if we want to store a second name?

$yourname = "Peter"

or as part of the array that you already made:

$myarray[1] = "Peter"

Again, we did the same thing. But to work with the plain variables we need to know two variable names. To do the same thing with the array we need only know one array name. Doesn't make much difference when we have only two. But what if we had ten, or a hundred, or an indefinite number of names to store? Then an array because way, way easier to manage because it can be of arbitrary size holding just one name or thousands.

Each has its place, but arrays are a very important way to hold data in a program.

scottalanmiller

So think of an array as a list of variables that don't have their own names. They are just "first array element", "second array element", "third array element" and so forth until the list is complete. If you don't know how many array elements you have it is easy to do a for loop through them...

foreach thing in my array do something

That's great because you need only know the array name. The foreach loop figures out how many things are in the array and does something with each one. If you had hundreds or thousands of individual variables that you wanted to do the same thing with, that would be a mess.

chutestrate

That makes sense.

chutestrate

For my current limited understanding arrays are easier to understand than than the $args

scottalanmiller

@chutestrate said:

For my current limited understanding arrays are easier to understand than than the $args

$args is just an array, nothing more.

scottalanmiller

Here is a little array program to do basically the same thing as above but using an array defined inside of the script rather than passing in arguments from the command line...

$myarray = "John", "Peter", "Linda", "Scott", "Norman", "Jenny"

for ($i=0; $i -lt $myarray.length; $i++) {
   'This is $myarray[' + $i + "], which is: " + $myarray[$i]
}

scottalanmiller

When you run it you get this...

> .\arraydemo.ps1
This is $myarray[0], which is: John
This is $myarray[1], which is: Peter
This is $myarray[2], which is: Linda
This is $myarray[3], which is: Scott
This is $myarray[4], which is: Norman
This is $myarray[5], which is: Jenny

chutestrate

@scottalanmiller said:

@chutestrate said:

For my current limited understanding arrays are easier to understand than than the $args

$args is just an array, nothing more.

don't follow that one.

scottalanmiller

So as you can see, I set the array to have those names in it with this line...

$myarray = "John", "Peter", "Linda", "Scott", "Norman", "Jenny"

When you use $args, the exact same thing is happening except that PowerShell is doing it automatically and hidden from you because it is happening from the command line and you don't write it out explicitly. But what is happening under the hood in a case where you do this...

.\myexample John Peter Linda Scott Norman Jenny

What PowerShell is doing without you having to write it is basically this...

$args = "John", "Peter", "Linda", "Scott", "Norman", "Jenny"

scottalanmiller

@chutestrate said:

$args is just an array, nothing more.

don't follow that one.

Not sure what else to say. It's that simple. $args is an array. $myarray is an array. There's nothing more to it. The only thing that makes $args special is that it is the one array that PowerShell makes for you when you run your script.

chutestrate

Not a problem. This has been phenomenal. I've learned a lot. I'll try to use this to understand the args. Unfortunately, I'm looping back to some of my original confusion. I know you addressed it, but it's not making completed sense.

scottalanmiller

Definitely leave $args for now and focus on arrays. Once you are solid on arrays, $args is pretty much self explanatory. Try doing some sample scripting with arrays for things. That will help a lot. In all seriousness, doing a MadLibs script is a good way to learn.

chutestrate

I'll do that.

scottalanmiller

I doubt that Martin will agree but I don't find PowerShell to be particularly well suited to learning programming concepts. It's a great language for what it is, but I'm very glad that I learned programming on other languages and then learning PowerShell.

chutestrate

I'm not fooling myself. I don't do well with trying to be a programmer. This is part of the testing goals. I just got interested in powershell, and am trying it out. Thank you for all the time. I'm rereading the posts, and I'm going to have a hard time matching $args to arrays. Maybe tomorrow it will click.