All posts by Jeffery Hicks

Friday Fun Reverse PowerShell

reverseThese Friday Fun posts are not supposed to be practical, yet hopefully still entertaining and educational. Today’s article is no exception but I ‘ll be you’ll try it at least once. And you’ll maybe even learn something about PowerShell that perhaps you didn’t know before. It all starts with a string. We use strings all the time for things like passwords and names. Let me start by explaining some basic concepts and then we’ll get to the fun stuff.

The string object has a number of methods, but I’m not going to use any of them today. Instead, I want to start by showing that the string is an array, or collection, of characters. This means you can access any element by its index number.

You can start at the end of the array with -1. You can also get several elements with the Range ( .. ) operator.

So, what about counting in reverse? We know we can start at -1. -2 would give us the 2nd to last element, -3 the third to last and so on. Therefore all we need to do is count backwards to the beginning.

I used the string length to know how far back to count. But wait, it gets better. Let’s bring in the -Join operator. This operator is designed to join elements of an array into a single string.

If you don’t want to specify a delimiter, you can use -Join like this:

See where I’m going with this? Let’s join the reversed array of string characters.

So if I can take any string and reverse it, why not reverse PowerShell? I created a function called Out-Reverse.

The idea is that you can run any PowerShell expression, pipe it to Out-Reverse, and you’ll get just that: reverse output.
out-reverse

The function takes any pipeline input and stores it in a temporary array. Once everything has been processed, the data is converted to a string with Out-String. Because I need to process each line separately, I split what would otherwise be a very long single string, into multiple strings on the end of line marker (`n).

$Text is now an array of strings and I can reverse each one.

It is kind of fun looking at reversed output. For you language geeks, this also makes a great palindrome tester.

Or maybe you need some simple obfuscation.

Actually, if you find a production-worthy use of this function I hope you’ll share it with me and the community. But as always I hope you picked up a PowerShell tidbit along the way that you can use in your “real” PowerShell work.

Enjoy your weekend. I’m sure you earned it.

Pimp your Prompt

bling2If you are like me and live in PowerShell, then you spend a great deal of your day looking at your PowerShell prompt. That little indicator in the console and ISE that usually shows where you are. That little part of your PowerShell world is defined by a built-in function called Prompt. You can easily see the function like this:

This prompt is from PowerShell v4 but I’m pretty sure it is the same function that was used in v3. PowerShell v2 has a different function.

Did you notice that the newer function has a help link? Try it:

help prompt -online

You’ll get the online version of the about_prompts help topic. The great thing about the prompt function is that you can change it. I’ve posted a variety of prompts over the years. But here are 4 more for you to try out. These prompts should work in v3 and later. Most of the functions are simple additions to the standard prompt and should work for both the console and ISE. To try out the prompt you can paste the function into your PowerShell session. To make it “permanent”, insert it into your PowerShell profile script.

Include PowerShell Version

This prompt inserts the PowerShell major version into your prompt.
version-prompt

Include Admin

This prompt will test if you are running as Admin and if so, it inserts [ADMIN] in red text.
adminprompt

Include Computername

Do you like how a remoting session shows you the computer you are connected to? Why not have that all the time? All I’ve done is insert the local computername from the Computername environmental variable.

computername-prompt

Auto Export Command History

This last version serves up a twist on transcription. When you run a transcript you get the command and results. But maybe all you want is a record of all the commands you ran. Sure, you could export command history at the end of your session, but you have to remember to do so and if you exceed your maximum history count, you’ll miss commands. In this prompt, everytime you hit enter, it gets the last command you ran and appends it to a log file. The log file is created in your PowerShell directory and uses the naming format of the PowerShell host, without spaces, a time stamp (YearMonthDay) and the process ID of the current PowerShell session. This allows you to keep multiple PowerShell sessions with separate logs. The log file will only record the command if it is different than the last one you ran. This also allows you to hit Enter without doing anything and not fill up your log.

If you temporarily paste in one of these Prompt functions, but don’t like it, you can simply restart PowerShell to get your original prompt. Or you can use this function to restore it.

This is handy to put into your PowerShell profile if you are experimenting with prompts. The Restore-Prompt simply defines a new Prompt function in the global scope. I’m using the default PowerShell prompt but you change it to whatever you wanted.

If you are doing something cool with your prompt, I hope you’ll share.

Friday Fun: A Random PowerShell Console

crayonsThis week I thought we’d have a little fun with the PowerShell console and maybe pick up a few scripting techniques along the way. Today I have a function that changes the foreground and background colors of your PowerShell console to random values. But because you might want to go back to your original settings without completing restarting PowerShell the function allows you to reset to your original values. Oh, and it also supports -Whatif. Here’s what I came up with.

The function will not work properly in the PowerShell ISE so I’ve included some code at the beginning to see if it is running in the ISE. If so, the command displays a warning and bails out. This is a scenario where using Return is completely acceptable as I want to return out of the pipeline without doing anything. I could have used a command like this: Return “This command only works in the PowerShell console.” but that would have written a string object to the pipeline and I don’t want anything to go to the pipeline. Plus, I prefer to use Write-Warning for messages like this.

When you run the command, it tests for the existence of some variables, $savedfg and $savedbg, that are defined in the global scope. You’ll notice the use of the global: prefix. If they are not defined, then the assumption is that this is the first time the command has been run and the variables will be defined with the current values of the $host.ui.rawui.foregroundcolor and $host.ui.rawui.backgroundcolor values. Later, if you use -Reset, the command will use these values to restore your original settings.

Otherwise, the command gets a random color for the System.ConsoleColor enumeration for the background and then another random color for the foreground, that is different than the randomly selected background color.

When you look at the code, you will see that I am specifying in the cmdletbinding attribute that the function supports ShouldProcess. That could also be written [cmdletbinding(SupportsShouldProcess=$True)] but that seems redundant to me. Anyway, the command to make the change, $host.ui.rawui.backgroundcolor= $bg, by itself doesn’t know anything about ShouldProcess and -WhatIf. But I can add my own code using an If statement.

The value for the ShouldProcess() method is the text you see as part of the “…performing operation on target…” message. The text is the target.
set-randomconsol-whatif

All I’ve done is define a variable, $msg, to make the line of code easier to read. As you can see, it is not that difficult to add your own support for -WhatIf. And now, if you get a little bored, mix it up for a fresh perspective. I’ve even included an alias, src, in case you have to type in a console where you can’t see what you’re typing.

Have a terrific weekend.