Most people I give this challenge to fail to account for the complexities of even a simple format like CSV, and typically simply use "grep" to find processes, which would cause havoc with simple user names like "Bob Ash = bash".

For comparison, the equivalent in PowerShell is this:

    #require -RunAsAdministrator
    $i = ConvertFrom-Csv @'
    UserName,ProcessName
    DOMAIN\BobJones,explorer
    DOMAIN\Bash,notepad
    '@
    
    $ps = Get-Process -IncludeUserName
    Compare-Object $ps $i -PassThru -Property UserName,ProcessName -ExcludeDifferent -IncludeEqual  `
        | Stop-Process -PassThru `
        | Sort-Object PeakWorkingSet64 -Descending `
        | Select-Object `
            ProcessName, `
            PeakWorkingSet64,`
            @{ Name='StartDate'; Expression={ '{0:o}' -f $_.StartTime } } `
        | ConvertTo-Csv

It's also a trivial extension to convert this snippet into a "ps1" script that can take formal parameters as input from anything that has those two columns, not just CSVs. And those parameters can be invoked manually, validated by the engine (not code!), and so forth.

What I hope this PowerShell version shows off is just how "neat" it is compared to bash. It's just a pipeline of little processing commands: "get,compare,stop,sort,select,convert". As impressive as your bash solution is, it's... messy. You were forced to write manual loops, use JSON for processing CSV, and do all sorts of admittedly pretty fancy trickery. Ask yourself: Could a junior tech make changes to your script and not break it? Could they even read it? I know I certainly couldn't, and I know more than a little bash!

As to how extensible PowerShell is: More than bash!

The "shell API" is just a byte stream in, and a bunch of byte streams out. That's it.

The PowerShell API is very rich, but it's also very easy to get started. You can simply write scripts or write a "binary module" in any .NET language such as C#. Simply derive from the System.Management.Automation.Cmdlet class, override the processing methods as required, and start writing code. The PowerShell engine will take care of things for you like hooking up input parameters, matching wild cards, expanding file paths, validating inputs, generating error messages in the user's OS language, etc...

In my experience, I can write a "proper" command line tool with all the bells & whistles using C/C++ in about a few thousand lines of code. With modern command-line parsing libraries, it's about 500 lines if I'm lucky. Meanwhile, it's possible to build the equivalent using PowerShell and C# in about 50 lines, of which 40 is just generic C# class boilerplate.

One of the things not often mentioned about PowerShell is its embeddability. I have explored this since writing https://news.ycombinator.com/item?id=22849569 .

    gci
    | select name

Not mentioned enough; Exchange 2007 GUI was built with PowerShell integration such that you could click through with a mouse, and it would show you the powershell code for you to copy/paste and reuse it yourself without a GUI. This is a very underused, under-discussed idea, IMHO.

Incidentally, I think it would have been possible to use only `csvkit` commands and skip the format munging to and from json, but I have an allergy to working with csvs since the format is a bit underspecified and there exist "csv" files that break even the few rules the format is supposed to have. You would be horrified at some of the things I have seen that called themselves "csv".

> In my experience, I can write a "proper" command line tool with all the bells & whistles using C/C++ in about a few thousand lines of code

Yeah, in my experience trying to write command line tools in low level languages is an exercise in pain. I usually write new tools in Python, where similar to your experience writing a simple command is ~20 lines of code, ~10 of which is boilerplate that is the same for every command.

That said, powershell does look pretty cool. And I see that it's possible to install on linux as well[1], and as far as I can tell even to write my commands in python[2], so it almost looks like "a unix-style shell but with types" which would be useful.

[1] https://docs.microsoft.com/en-us/powershell/scripting/instal... [2] http://pythonnet.github.io/